[issue17005] Add a topological sort algorithm
Paddy McCarthy added the comment: Please ignore my earlier Message-id <1598493715.04.0.06462575371.issue17...@roundup.psfhosted.org>. I missed a dependency in cutting down a larger example. Sorry. -- ___ Python tracker <https://bugs.python.org/issue17005> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue17005] Add a topological sort algorithm
Paddy McCarthy added the comment:
I've been playing with Python 3.9.0rc1 and was looking at a particular graph to
see when it released tasks for processing.
I ran the following code:
from functools import reduce
from pprint import pprint as pp
from collections import defaultdict
from graphlib import TopologicalSorter
from heapq import heapify, heappush, heappop, heappushpop
print("""
###
### TASK DEPENDENCY
###
A -> B -> C
↓↓↓
D -> E -> F
""")
graph3 = {"A": {"B", "D"},
"B": {"C", "E"},
"C": {"F"},
"D": {"E"},
"E": {"F"},
}
tasktime = {task: 2 for task in 'ABCDEF'}
def simulate(graph, tasktime):
print("\n## NEW SIMULATION")
t = 0
heap = []
heapify(heap)
print("\n# Task runtimes:")
for node, tm in tasktime.items():
print(f" {node}: {tm}")
print("\n# OUTPUT. (:> for task start times, <: for stop times).\n")
ts = TopologicalSorter(graph)
ts.prepare()
while ts.is_active():
for node in ts.get_ready():
finish = t + tasktime[node]
heappush(heap, (finish, node))
print(f"{' ' * t}{node}:> @{t}")
t, node = heappop(heap)
print(f"{' ' * t}{node}<: @{t}")
ts.done(node)
simulate(graph3, tasktime)
tasktime['C'] = 1
simulate(graph3, tasktime)
I got the following output:
###
### TASK DEPENDENCY
###
A -> B -> C
↓↓↓
D -> E -> F
## NEW SIMULATION
# Task runtimes:
A: 2
B: 2
C: 2
D: 2
E: 2
F: 2
# OUTPUT. (:> for task start times, <: for stop times).
F:> @0
F<: @2
C:> @2
E:> @2
C<: @4
E<: @4
B:> @4
D:> @4
B<: @6
D<: @6
A:> @6
A<: @8
## NEW SIMULATION
# Task runtimes:
A: 2
B: 2
C: 1
D: 2
E: 2
F: 2
# OUTPUT. (:> for task start times, <: for stop times).
F:> @0
F<: @2
C:> @2
E:> @2
C<: @3
E<: @4
B:> @4
D:> @4
B<: @6
D<: @6
A:> @6
A<: @8
>>>
Note that in the second simulation, C finish, but B isn't then immediately
started. I have my own code that also works like this but it isn't optimal.
Thanks guys.
--
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[issue33235] Better help text for dict.setdefault
New submission from Paddy McCarthy <paddy3...@gmail.com>: Hi, I was answering some question and used dict.setdefault as part of the solution and posted the help() on it as part of my answer. The help was this: In [15]: help(mapper.setdefault) Help on built-in function setdefault: setdefault(...) method of builtins.dict instance D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D This seems the wrong way around. Is it not better expressed as D.setdefault(k[,d]) -> set D[k]=d if k not in D and then D.get(k,d) -- assignee: docs@python components: Documentation messages: 315015 nosy: Paddy McCarthy, docs@python priority: normal severity: normal status: open title: Better help text for dict.setdefault type: enhancement versions: Python 3.6 ___ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue33235> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24914] Python: Not just OO style but this is not mentioned on python.org or in FAQ
Paddy McCarthy added the comment: OK, here's a suggested re-wording: Python is an interpreted, interactive, object-oriented programming language that also supports programming in procedural and functional styles. It incorporates modules, exceptions, dynamic typing, very high level dynamic data types, and classes; but statements are not required to be contained in class definitions and functions are first class - being able to be composed, returned from other functions and be a member of other container types such as dicts, sets, and lists. If that is too long,an alternative would be to delete my addition to the last sentence from ; but classes are not ... Leaving it to the reader to research just how procedural and functional Python can be. (Where should a programmer, but newbie-to-Python look)? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24914 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue24914] Python: Not just OO style but this is not mentioned on python.org or in FAQ
New submission from Paddy McCarthy: Just read http://www.ibmsystemsmag.com/ibmi/developer/general/different-world-python/?utm_campaign=ibm-enewsutm_medium=emailutm_source=ibmi-jul22-2015?utm_content=exclusive1-headline It states that they could have had an officially supported version of Python on that IBM platform much earlier but for this: The second was that everything we read on Python, and all the examples we encountered, led us to believe that it was a completely object oriented (OO) language They may have used it earlier had they known then that Python can be written in a procedural style they having no love of Java's OO, but being able to use PHP and access PHP's OO bits. Looking again on python.org, the examples are not OO, but when you delve down, say to the FAQ - it gives the mistaken impression that OO is the _only_ style of programming supported: https://docs.python.org/2/faq/general.html#what-is-python Somehow we need to explain that OO is an implementation style, but the language allows code to be written in just as much - or as little, of proceedural/OO/functional styles as the programmer is comfortable with. -- assignee: docs@python components: Documentation messages: 248987 nosy: Paddy McCarthy, docs@python priority: normal severity: normal status: open title: Python: Not just OO style but this is not mentioned on python.org or in FAQ type: enhancement ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue24914 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Re: Need opinions on P vs NP
On Saturday, 18 April 2015 08:09:06 UTC+1, wxjm...@gmail.com wrote: Le samedi 18 avril 2015 03:19:40 UTC+2, Paddy a écrit : Having just seen Raymond's talk on Beyond PEP-8 here: https://www.youtube.com/watch?v=wf-BqAjZb8M, it reminded me of my own recent post where I am soliciting opinions from non-newbies on the relative Pythonicity of different versions of a routine that has non-simple array manipulations. The blog post: http://paddy3118.blogspot.co.uk/2015/04/pythonic-matrix-manipulation.html The first, (and original), code sample: def cholesky(A): L = [[0.0] * len(A) for _ in range(len(A))] for i in range(len(A)): for j in range(i+1): s = sum(L[i][k] * L[j][k] for k in range(j)) L[i][j] = sqrt(A[i][i] - s) if (i == j) else \ (1.0 / L[j][j] * (A[i][j] - s)) return L The second equivalent code sample: def cholesky2(A): L = [[0.0] * len(A) for _ in range(len(A))] for i, (Ai, Li) in enumerate(zip(A, L)): for j, Lj in enumerate(L[:i+1]): s = sum(Li[k] * Lj[k] for k in range(j)) Li[j] = sqrt(Ai[i] - s) if (i == j) else \ (1.0 / Lj[j] * (Ai[j] - s)) return L The third: def cholesky3(A): L = [[0.0] * len(A) for _ in range(len(A))] for i, (Ai, Li) in enumerate(zip(A, L)): for j, Lj in enumerate(L[:i]): #s = fsum(Li[k] * Lj[k] for k in range(j)) s = fsum(Lik * Ljk for Lik, Ljk in zip(Li, Lj[:j])) Li[j] = (1.0 / Lj[j] * (Ai[j] - s)) s = fsum(Lik * Lik for Lik in Li[:i]) Li[i] = sqrt(Ai[i] - s) return L My blog post gives a little more explanation, but I have yet to receive any comments on relative Pythonicity. def cholesky999(A): n = len(A) L = [[0.0] * n for i in range(n)] for i in range(n): for j in range(i+1): s = 0.0 for k in range(j): s += L[i][k] * L[j][k] if i == j: L[i][j] = sqrt(A[i][i] - s) else: L[i][j] = (1.0 / L[j][j] * (A[i][j] - s)) return L Simple, clear, logical, consistant. And so most Pythonic? Maybe so. -- https://mail.python.org/mailman/listinfo/python-list
Re: Need opinions on P vs NP
On Saturday, 18 April 2015 03:34:57 UTC+1, Ian wrote: On Fri, Apr 17, 2015 at 7:19 PM, Paddy paddy3...@..l.com wrote: Having just seen Raymond's talk on Beyond PEP-8 here: https://www.youtube.com/watch?v=wf-BqAjZb8M, it reminded me of my own recent post where I am soliciting opinions from non-newbies on the relative Pythonicity of different versions of a routine that has non-simple array manipulations. The blog post: http://paddy3118.blogspot.co.uk/2015/04/pythonic-matrix-manipulation.html The first, (and original), code sample: def cholesky(A): L = [[0.0] * len(A) for _ in range(len(A))] for i in range(len(A)): for j in range(i+1): s = sum(L[i][k] * L[j][k] for k in range(j)) L[i][j] = sqrt(A[i][i] - s) if (i == j) else \ (1.0 / L[j][j] * (A[i][j] - s)) return L The second equivalent code sample: def cholesky2(A): L = [[0.0] * len(A) for _ in range(len(A))] for i, (Ai, Li) in enumerate(zip(A, L)): for j, Lj in enumerate(L[:i+1]): s = sum(Li[k] * Lj[k] for k in range(j)) Li[j] = sqrt(Ai[i] - s) if (i == j) else \ (1.0 / Lj[j] * (Ai[j] - s)) return L The third: def cholesky3(A): L = [[0.0] * len(A) for _ in range(len(A))] for i, (Ai, Li) in enumerate(zip(A, L)): for j, Lj in enumerate(L[:i]): #s = fsum(Li[k] * Lj[k] for k in range(j)) s = fsum(Lik * Ljk for Lik, Ljk in zip(Li, Lj[:j])) Li[j] = (1.0 / Lj[j] * (Ai[j] - s)) s = fsum(Lik * Lik for Lik in Li[:i]) Li[i] = sqrt(Ai[i] - s) return L My blog post gives a little more explanation, but I have yet to receive any comments on relative Pythonicity. I prefer the first version. You're dealing with mathematical formulas involving matrices here, so subscripting seems appropriate, and enumerating out rows and columns just feels weird to me. That said, I also prefer how the third version pulls the last column of each row out of the inner loop instead of using a verbose conditional expression that you already know will be false for every column except the last one. Do that in the first version, and I think you've got it. But shouldn't the maths transcend the slight change in representation? A programmer in the J language might have a conceptually neater representation of the same thing due to its grounding in arrays (maybe) and for a J representation it would become J-thonic. In Python, it is usual to iterate over collections and also to use enumerate where we must have indices. Could it be that there is a also a strong pull in the direction of using indices because that is what is predominantly given in the way matrix maths is likely to be expressed mathematically? A case of TeX likes indices so we should too? -- https://mail.python.org/mailman/listinfo/python-list
Need opinions on P vs NP
Having just seen Raymond's talk on Beyond PEP-8 here: https://www.youtube.com/watch?v=wf-BqAjZb8M, it reminded me of my own recent post where I am soliciting opinions from non-newbies on the relative Pythonicity of different versions of a routine that has non-simple array manipulations. The blog post: http://paddy3118.blogspot.co.uk/2015/04/pythonic-matrix-manipulation.html The first, (and original), code sample: def cholesky(A): L = [[0.0] * len(A) for _ in range(len(A))] for i in range(len(A)): for j in range(i+1): s = sum(L[i][k] * L[j][k] for k in range(j)) L[i][j] = sqrt(A[i][i] - s) if (i == j) else \ (1.0 / L[j][j] * (A[i][j] - s)) return L The second equivalent code sample: def cholesky2(A): L = [[0.0] * len(A) for _ in range(len(A))] for i, (Ai, Li) in enumerate(zip(A, L)): for j, Lj in enumerate(L[:i+1]): s = sum(Li[k] * Lj[k] for k in range(j)) Li[j] = sqrt(Ai[i] - s) if (i == j) else \ (1.0 / Lj[j] * (Ai[j] - s)) return L The third: def cholesky3(A): L = [[0.0] * len(A) for _ in range(len(A))] for i, (Ai, Li) in enumerate(zip(A, L)): for j, Lj in enumerate(L[:i]): #s = fsum(Li[k] * Lj[k] for k in range(j)) s = fsum(Lik * Ljk for Lik, Ljk in zip(Li, Lj[:j])) Li[j] = (1.0 / Lj[j] * (Ai[j] - s)) s = fsum(Lik * Lik for Lik in Li[:i]) Li[i] = sqrt(Ai[i] - s) return L My blog post gives a little more explanation, but I have yet to receive any comments on relative Pythonicity. -- https://mail.python.org/mailman/listinfo/python-list
[issue10395] new os.path function to extract common prefix based on path components
Paddy McCarthy added the comment: Can we now: 1. Move os.path.commonprefix to str.commonprefix or string.commonprefix 2. Deprecate the use of os.path.commonprefix 3. Add os.path.commonpath 4. Update the documentation. This seems to have lingered for too long and yet people have been willing to do the work it seems (from 1999). -- nosy: +Paddy McCarthy ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue10395 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23695] idiom for clustering a data series into n-length groups
Paddy McCarthy added the comment: I like R. David Murray's suggestion, but I am also aware of how it works and so cannot judge how it would look to the intermediate Python programmer who knows iterators and zip, but is new to this grouper; (who I think should be the target audience). -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23695 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23695] idiom for clustering a data series into n-length groups
Paddy McCarthy added the comment: Hmmm. It seems that the problem isn't to do with the fact that it works, or how to apply it; the problem is with *how* it works. Making it an idiom means that too many will use it without knowing why it works which could lead to later maintenance issues. I think a better description of how it works may be needed for the docs. Unfortunately my description of the how at http://paddy3118.blogspot.co.uk/2012/12/that-grouping-by-zipiter-trick-explained.html was not written with the docs in mind, but you are welcome to any part or the whole, for the Python docs. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23695 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23695] idiom for clustering a data series into n-length groups
New submission from Paddy McCarthy: In the zip section of the documentation, e.g. https://docs.python.org/3/library/functions.html#zip There is mention of an idiom for clustering a data series into n-length groups that I seem to only come across when people are explaining how it works on blog entries such as the three mentioned here: http://www.reddit.com/r/programming/comments/2z4rv4/a_function_for_partitioning_python_arrays/cpfvwun?context=3 It is not a straight-forward bit of code and so I think it should either be explained in more detail in the documentation or removed as an idiom, or I guess it could be encapsulated in a function and added to the stdlib. -- assignee: docs@python components: Documentation messages: 238365 nosy: Paddy McCarthy, docs@python priority: normal severity: normal status: open title: idiom for clustering a data series into n-length groups type: enhancement versions: Python 2.7, Python 3.2, Python 3.3, Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23695 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Re: Bug in timsort!?
On Wednesday, 25 February 2015 00:08:32 UTC, Chris Angelico wrote: On Wed, Feb 25, 2015 at 10:50 AM, Skip Montanaro skip.mo...@gmail.com wrote: Even if/when we get to the point where machines can hold an array of 2**49 elements, I suspect people won't be using straight Python to wrangle them. snip Would it be sufficient to stick a comment into the source saying This may have problems with lists in excess of 2**49 elements, and leave it until that's actually likely to happen? ChrisA If we are given a proven fix with little downside then if we are to touch the source then we should MAKE THE FIX. To do otherwise would send the wrong signal to those that depend on the perceived integrity of the C-Python developers. -- https://mail.python.org/mailman/listinfo/python-list
Re: Natural use of cmp= in sort
On Tuesday, 11 November 2014 18:07:27 UTC, Ian wrote: The example that I posted is one that I recall being brought up on this list in the past, but I don't have a link for you. THanks Ian for your help in this. -- https://mail.python.org/mailman/listinfo/python-list
Re: Natural use of cmp= in sort
On Tuesday, 11 November 2014 09:07:14 UTC, Ian wrote: On Tue, Nov 11, 2014 at 12:44 AM, Paddy paddyxxx-at-xmail.com wrote: Thanks Ian. The original author states ...and it is sure that the given inputs will give an output, i.e., the inputs will always be valid., which could be taken as meaning that all inputs are sufficient, well formed, and contain all relations as their first example does. Well, I brought it up because the start of that sentence is There can be multiple inequalities as answer but I need any one which is correct The only way there would be more than one correct answer would be if the inputs were only partially ordered. I take the second part of the sentence as meaning only that the input can be safely assumed to be consistent. Yes, I knew that there are cases where a cmp function is more natural than key; the idea is to squirrel out a few. We have already made the, (well reasoned in my opinion), decision to go down the key= route in Python 3. I also like to track where my algorithms might originally map to cmp=. (It is not often). Basically any time you have a comparison that isn't easily expressed by mapping the values to some bunch of ordered objects. Yep. I want to track when this comes up for me and others during their normal programming rather than in examples made to highlight the issue. -- https://mail.python.org/mailman/listinfo/python-list
Natural use of cmp= in sort
Hi, I do agree with
Raymond H. about the relative merits of cmp= and key= in
sort/sorted, but I decided to also not let natural uses of cmp= pass silently.
In answering this question, http://stackoverflow.com/a/26850434/10562 about
ordering subject to inequalities it seemed natural to use the cmp= argument of
sort rather than key=.
The question is about merging given inequalities to make 1 inequality such that
the inequalities also stays true.
Here is a copy of my code:
Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)] on
win32
Type copyright, credits or license() for more information.
ineq = f4 f2 f3
f4 f1 f3
f4 f2 f1
f2 f1 f3
print(ineq)
f4 f2 f3
f4 f1 f3
f4 f2 f1
f2 f1 f3
greater_thans, all_f = set(), set()
for line in ineq.split('\n'):
tokens = line.strip().split()[::2]
for n, t1 in enumerate(tokens[:-1]):
for t2 in tokens[n+1:]:
greater_thans.add((t1, t2))
all_f.add(t1)
all_f.add(t2)
sorted(all_f, cmp=lambda t1, t2: 0 if t1==t2 else
...(1 if (t1, t2) not in greater_thans else -1))
['f4', 'f2', 'f1', 'f3']
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Re: Natural use of cmp= in sort
On Monday, 10 November 2014 19:44:39 UTC, Ian wrote:
On Mon, Nov 10, 2014 at 12:19 PM, Peter Otten xxx@yyy wrote:
I'm not sure this works. I tried:
Here's a simpler failure case.
ineq = f2 f3
... f3 f1
[Previously posted code elided]
greater_thans
set([('f3', 'f1'), ('f2', 'f3')])
sorted(all_f, cmp=lambda t1, t2: 0 if t1==t2 else
... (1 if (t1, t2) not in greater_thans else -1))
['f1', 'f2', 'f3']
Note that the greater_thans set is missing the implication by
transitivity that f2 f1, so the given cmp function would
inconsistently return -1 for both comparisons cmp('f1', 'f2') and
cmp('f2', 'f1').
Thanks. I will look into this...
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Re: Natural use of cmp= in sort
On Monday, 10 November 2014 18:45:15 UTC, Paddy wrote: Hi, I do agree with Raymond H. about the relative merits of cmp= and key= in sort/sorted, but I decided to also not let natural uses of cmp= pass silently. In answering this question, http://stackoverflow.com/a/26850434/10562 about ordering subject to inequalities it seemed natural to use the cmp= argument of sort rather than key=. The question is about merging given inequalities to make 1 inequality such that the inequalities also stays true. Thanks Peter, Ian. I have modified my code to expand transitive relations and ask you to view it on stackoverflow via the original link (as posting code on newsgroups is an ugly hack). My main reason for the post to c.l.p remains though; it seems like a *natural* use of the cmp= comparator function to sorted rather than using key= . -- https://mail.python.org/mailman/listinfo/python-list
Re: Natural use of cmp= in sort
On Tuesday, 11 November 2014 06:37:18 UTC, Ian wrote:
On Mon, Nov 10, 2014 at 8:09 PM, Paddy paddyxxx-at-xmail.com wrote:
On Monday, 10 November 2014 18:45:15 UTC, Paddy wrote:
Hi, I do agree with
Raymond H. about the relative merits of cmp= and key= in
sort/sorted, but I decided to also not let natural uses of cmp= pass
silently.
In answering this question, http://stackoverflow.com/a/26850434/10562
about ordering subject to inequalities it seemed natural to use the cmp=
argument of sort rather than key=.
The question is about merging given inequalities to make 1 inequality such
that the inequalities also stays true.
Thanks Peter, Ian. I have modified my code to expand transitive relations
and ask you to view it on stackoverflow via the original link (as posting
code on newsgroups is an ugly hack).
You still run into trouble though if the given inequalities don't
provide enough information for a total ordering. E.g.:
' '.join(extract_relations(f4 f1
... f2 f3))
'f1 f2 f3 f4'
By adding some debugging prints, we can see what cmp calls were made
by the sort routine and what the results were:
cmp('f2', 'f1') - 1
cmp('f3', 'f2') - 1
cmp('f4', 'f3') - 1
There is no information about the relative order of f2 and f1, so the
cmp function just returns 1 there.
f2 is known to be greater than f3, so that call correctly returns 1.
There is again no information about the relative order of f4 and f3,
so it again just returns 1. However, this is inconsistent with the
first comparison that placed f1 f2, because it implies that f1 f4.
As you can see, giving an inconsistent cmp function to sort produces
bogus results. If you only have a partial ordering of the inputs, you
need to make sure that the cmp function you provide is consistent with
*some* total ordering.
Another issue is that your expand_transitive_relations function is I
think O(n**3 log n), which looks unattractive compared to the O(n**2)
topological sort given in the other answers. Another advantage of the
topological sort is that it will detect if the graph is cyclic (i.e.
the input data itself is inconsistent), rather than just return a
bogus output.
My main reason for the post to c.l.p remains though; it seems like a
*natural* use of the cmp= comparator function to sorted rather than using
key= .
There are cases where a cmp function is more natural than a key
function, but for these we have the functools.cmp_to_key adapter.
Thanks Ian. The original author states ...and it is sure that the given inputs
will give an output, i.e., the inputs will always be valid., which could be
taken as meaning that all inputs are sufficient, well formed, and contain all
relations as their first example does.
In that case, expand_transitive_relations is not even needed. Lets say it isn't
for the sake of argument, then we are left with the direct use of cmp= versus a
conversion to a key= function.
It seems to me that *in this case* the cmp= function naturally flows from the
solution algorithm and that cmp_to_key is less so.
Yes, I knew that there are cases where a cmp function is more natural than key;
the idea is to squirrel out a few. We have already made the, (well reasoned in
my opinion), decision to go down the key= route in Python 3. I also like to
track where my algorithms might originally map to cmp=. (It is not often).
My only other case of this type is here:
http://stackoverflow.com/questions/15797120/can-this-cmp-function-be-better-written-as-a-key-for-sorted.
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[issue16580] Add examples to int.to_bytres and int.from_bytes
Paddy McCarthy added the comment: On 06/12/2012 14:31, Ezio Melotti wrote: Ezio Melotti added the comment: I agree. The examples in the doc seem clear to me, whereas the ones you proposed are not as clear. Do you think there's something that they don't currently cover that should be added? -- nosy: +ezio.melotti ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue16580 ___ First, Thanks Ezio and Andrew for your replies. My problem was that when working on bitcoin address validation I saw code that was shifting and 'ing with 0xFF to convert to multiple bytes and half remembered that there might be a Python function to do that. On finding the .to_bytes method and its parameter big or little, the only way I had of working out which to use was to try each until I found out which worked. I therefore thought that what would have helped me was code that showed the equivalent expanded Python for the method in a similar way to what is done for some of the itertools functions etc. If we split my request into two: 1. Is such extra explanation necessary. 2. Is my specific code that extra explanation. I can work on the code a bit more. Have I persuaded you that an extra explanation is necessary? Thanks, Paddy. P.S. I guess what is currently present shows the result of the methods but nothing on how it could be generated. I am stating that the generation can aid comprehension. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue16580 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue16580] Add examples to int.to_bytres and int.from_bytes
Paddy McCarthy added the comment: On 09/12/2012 10:55, Ezio Melotti wrote: Ezio Melotti added the comment: Usually we add plain Python equivalents when they are simple enough that the code equivalent is as understandable as the prose or more (see for example http://docs.python.org/3/library/functions.html#all, or the itertools functions you mentioned). For this case I think it would help if you presented an equivalent function, e.g.: def to_bytes(n, length, order): if order == 'little': return bytes((n i*8) 0xff for i in range(length)) elif order == 'big': return bytes((n i*8) 0xff for i in reversed(range(length))) or even: def to_bytes(n, length, order): indexes = range(length) if order == 'little' else reversed(range(length)) return bytes((n i*8) 0xff for i in indexes) This is also done for http://docs.python.org/3.3/library/stdtypes.html#int.bit_length just above to/from_bytes, so it might be a good addition. If this is done, the equivalent function can also be added to the test suite, so we can verify that it's indeed equivalent. -- keywords: +easy stage: - needs patch versions: +Python 2.7, Python 3.2, Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue16580 ___ The second example looks great. I like the dual use for testing too and will try and remember both the next time I find I have ireas about the documentation. Thanks guys. It's appreciated! -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue16580 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue16580] Add examples to int.to_bytres and int.from_bytes
New submission from Paddy McCarthy: http://docs.python.org/3.3/library/stdtypes.html?highlight=to_bytes#int.to_bytes and http://docs.python.org/3.3/library/stdtypes.html?highlight=to_bytes#int.to_bytes would benefit from an example showing what they do based on simpler coding. I have such an example that I wrote here: http://paddy3118.blogspot.co.uk/2012/11/some-identities-for-python-inttobytes.html that you can use. I.e. n = 2491969579123783355964723219455906992268673266682165637887 length = 25 n2bytesbig= n.to_bytes(length, 'big') n2byteslittle = n.to_bytes(length, 'little') assert n2bytesbig== bytes( (n i*8) 0xff for i in reversed(range(length))) assert n2byteslittle == bytes( (n i*8) 0xff for i in range(length)) assert n == sum( n2bytesbig[::-1][i] i*8 for i in range(length) ) assert n == sum( n2byteslittle[i] i*8 for i in range(length) ) assert n == int.from_bytes(n2bytesbig,byteorder='big') assert n == int.from_bytes(n2byteslittle, byteorder='little') -- assignee: docs@python components: Documentation messages: 176671 nosy: docs@python, paddy3118 priority: normal severity: normal status: open title: Add examples to int.to_bytres and int.from_bytes type: enhancement versions: Python 3.3 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue16580 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Python 3.X: nonlocal support in eval/exec?
We can access nonlocal variables in a function, but if we were to eval/ exec the function we cannot set up a nested stack of evironment dicts. We are limited to just two: global and local. How about eval/exec take a new env argument that is a nested dictionary whose outer level corresponds to locals, and which has a __up__ value which is the next outer level environment dict. The outermost level of the nested dictionary would correspond to the global level? I haven't given much thought to my suggested solution - I just didn't want to leave a possible solution out. The major point is that there seems to be no support for nonlocal in eval/exec (unless, trivially, nonlocal==global). - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python 3.X: nonlocal support in eval/exec?
On Aug 11, 8:48 am, Terry Reedy tjre...@udel.edu wrote: On 8/11/2011 3:19 AM, Paddy wrote: We can access nonlocal variables in a function, but if we were to eval/ exec the function we cannot set up a nested stack of evironment dicts. We are limited to just two: global and local. Right. That was and is Python's execution model. Note that when you exec code, including a function call, the locals passed is the local context in which the code is executed. It is not the locals of any particular function called by the exec-ed code. If you exec a function that is a closure, the closure or non-local objects come with the function. A 'stack of dicts' has nothing to do with how function and nested funcs operate. -- Terry Jan Reedy Thanks Terry. -- http://mail.python.org/mailman/listinfo/python-list
Re: Testing for performance regressions
In an extended case when you try and capture how a function works over a range of inputs, you might want to not assume some relationship between input size and time, as this mnight limit your ability to change algorithms and still have acceptable performance. I.e. instead of this: input_range = (MIN, AVERAGE, MAX) for i in inpute_range: ..baseline = Timer(simple_func(i)).timeit() ..time_taken = Timer(my_func(i)).timeit() ..assert time_taken = simple_relation(i) * baseline It might be better to do this: input_range = (MIN_R, AVERAGE_R, MAX_R) time_ranges = (MIN_T, AVERAGE_T, MAX_T) for i,t in zip(inpute_range, time_ranges): ..baseline = Timer(simple_func(i)).timeit() ..time_taken = Timer(my_func(i)).timeit() ..assert time_taken = t * baseline This comes from electronic circuit design where designs must be proven to work over a range for different values for example voltage ranges and temperature ranges. The action of the function being timed might not be simple, for example if my_func swapped algorithms depending on its input to favour the average case. -- http://mail.python.org/mailman/listinfo/python-list
Re: Guido rethinking removal of cmp from sort method
On Tuesday, April 5, 2011 2:16:07 AM UTC+1, harrismh777 wrote: Steven D'Aprano wrote: I prefer to consider Python 2.7 and Python 3.x as different dialects of the same language. There are a very few handful of incompatibilities, most of which can be automatically resolved by the 2to3 fixers. Yes, I am actually finding this to be consistent with my experience of trying to come up to speed with 3.2. I have been relieved to find that less has changed than the fear-mongering and bickering was leading me to believe. Another item that would be nice as an IDLE enhancement would be a menu option that applies the fixers (either direction depending on version 2.7 -- 3.2) right in the IDE. Entries that could not be fixed could be flagged for manual update. If there are good tools for app developers to use to make the transition smoother then the development community won't get their ear chewed off so ragged, I'm supposing. Hats off and three cheers to the developers and python community as a whole, as some are down to sugesting easier access to 2-3 rather than OMG! How do I port!! Now that is an excellent sign that Python works. -- http://mail.python.org/mailman/listinfo/python-list
functools.partial doesn't work without using named parameter
Hi, I just found the following oddity where for function fsf1 I am forced to
use a named parameter for correct evaluation and was wondering why it doesn't
work, yet the example from the docs of wrapping int to create basetwo doesn't
need this?
The example:
from functools import partial
basetwo = partial(int, base=2)
basetwo('10010')
18
def fs(f, s): return [f(value) for value in s]
def f1(value): return value * 2
s = [0, 1, 2, 3]
fs(f1, s)
[0, 2, 4, 6]
fsf1 = partial(fs, f=f1)
fsf1(s)
Traceback (most recent call last):
File pyshell#24, line 1, in module
fsf1(s)
TypeError: fs() got multiple values for keyword argument 'f'
# BUT
fsf1(s=s)
[0, 2, 4, 6]
Would someone help?
- Thanks in advance, Paddy.
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Re: functools.partial doesn't work without using named parameter
P.S: Python 3.2! -- http://mail.python.org/mailman/listinfo/python-list
Re: functools.partial doesn't work without using named parameter
Thanks Ian, Benjamin, and Steven. I now know why it works as it does. Thinking about it a little more, Is it reasonable to *expect* partial acts as it does, rather than this way being an implementation convenience? (That was written as a straight question not in any way as a dig). I had thought that partial had enough information to, and would in fact, remove named parameter f from the signature of fsf1 returning something that could be called that is the equivalent of: def fsf1_( s ): ... I accept that that is not done, but would welcome discussion on if my expectation above was reasonable. Thanks guys :-) -- http://mail.python.org/mailman/listinfo/python-list
Re: functools.partial doesn't work without using named parameter
Aha! Thanks Ian for this new snippet. It is what I will use for my current example. (But please see my third posting on this too). -- http://mail.python.org/mailman/listinfo/python-list
Whats new in Python 3: concurrent-futures example error?
I just noted the example here: http://docs.python.org/dev/whatsnew/3.2.html#pep-3148-the-concurrent-futures-module import concurrent.futures, shutil with concurrent.futures.ThreadPoolExecutor(max_workers=4) as e: e.submit(shutil.copy, 'src1.txt', 'dest1.txt') e.submit(shutil.copy, 'src2.txt', 'dest2.txt') e.submit(shutil.copy, 'src3.txt', 'dest3.txt') e.submit(shutil.copy, 'src3.txt', 'dest4.txt') Should the last line show a copy of src4.txt rather than src3.txt going to dest4.txt? - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Whats new in Python 3: concurrent-futures example error?
My thanks. -- http://mail.python.org/mailman/listinfo/python-list
Re: EXOR or symmetric difference for the Counter class
On 17 Aug, 02:29, Raymond Hettinger pyt...@rcn.com wrote:
[Paddy]
Lets say you have two *sets* of integers representing two near-copies
of some system, then a measure of their difference could be calculated
as:
len(X.symmetric_difference(Y)) / (len(X) + len(Y)) * 100 %
If the two collections of integers are allowed duplicates then you
need a Counter/bag/multi-set type and the diff calculation I gave
originally.
Thanks for sharing your use case.
It's unlikely that I will add this method to the Counter API because
the rarity of use case does not warrant the added API complexity.
IMO, adding a method like this makes the class harder to learn,
understand and remember. It doesn't seem like much of a win over
using the existing alternatives:
* (b - c) + (c - b)
* (b | c) - (b c)
* DIY using the two counters as simple dicts
* writing a subclass providing additional binary operations
I would like to see someone post a subclass to the ASPN Cookbook that
adds a number of interesting, though not common operations. Your
symmetric_difference() method could be one. A dot_product() operation
could be another. Elementwise arithmetic is another option (we
already have add and subtract, but could possibly use multiply,
divide, etc). Scaling operations are another possibility (multiple
all elements by five, for example).
The Counter() class has low aspirations. It is a dictionary that
fills-in missing values with zero and is augmented by a handful of
basic methods for managing the counts.
Raymond
I created this that could be an addition to the bottom of the Python 3
collections.Counter class definition:
def __xor__(self, other):
''' symmetric difference: Subtract count, but keep only abs
results with non-zero counts.
Counter('abbbc') ^ Counter('bccd')
Counter({'b': 2, 'a': 1, 'c': 1, 'd': 1})
a, b = Counter('abbbc'), Counter('bccd')
(a-b) + (b - a) == a ^ b
True
'''
if not isinstance(other, Counter):
return NotImplemented
result = Counter()
for elem in set(self) | set(other):
newcount = self[elem] - other[elem]
if newcount != 0:
result[elem] = newcount if newcount 0 else -newcount
return result
- Paddy.
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Re: EXOR or symmetric difference for the Counter class
On Aug 17, 10:47 pm, Paddy paddy3...@googlemail.com wrote:
On 17 Aug, 02:29, Raymond Hettinger pyt...@rcn.com wrote:
[Paddy]
Lets say you have two *sets* of integers representing two near-copies
of some system, then a measure of their difference could be calculated
as:
len(X.symmetric_difference(Y)) / (len(X) + len(Y)) * 100 %
If the two collections of integers are allowed duplicates then you
need a Counter/bag/multi-set type and the diff calculation I gave
originally.
Thanks for sharing your use case.
It's unlikely that I will add this method to the Counter API because
the rarity of use case does not warrant the added API complexity.
IMO, adding a method like this makes the class harder to learn,
understand and remember. It doesn't seem like much of a win over
using the existing alternatives:
* (b - c) + (c - b)
* (b | c) - (b c)
* DIY using the two counters as simple dicts
* writing a subclass providing additional binary operations
I would like to see someone post a subclass to the ASPN Cookbook that
adds a number of interesting, though not common operations. Your
symmetric_difference() method could be one. A dot_product() operation
could be another. Elementwise arithmetic is another option (we
already have add and subtract, but could possibly use multiply,
divide, etc). Scaling operations are another possibility (multiple
all elements by five, for example).
The Counter() class has low aspirations. It is a dictionary that
fills-in missing values with zero and is augmented by a handful of
basic methods for managing the counts.
Raymond
I created this that could be an addition to the bottom of the Python 3
collections.Counter class definition:
def __xor__(self, other):
''' symmetric difference: Subtract count, but keep only abs
results with non-zero counts.
Counter('abbbc') ^ Counter('bccd')
Counter({'b': 2, 'a': 1, 'c': 1, 'd': 1})
a, b = Counter('abbbc'), Counter('bccd')
(a-b) + (b - a) == a ^ b
True
'''
if not isinstance(other, Counter):
return NotImplemented
result = Counter()
for elem in set(self) | set(other):
newcount = self[elem] - other[elem]
if newcount != 0:
result[elem] = newcount if newcount 0 else -newcount
return result
- Paddy.
And heres the cartesian product/multiply:
def __mul__(self, other):
'''Multiply counts by an integer; or cartesioan product
of two counters.
Counter('abbb') * 3
Counter({'b': 9, 'a': 3})
Counter('12') * Counter('21')
Counter({('2', '1'): 1, ('1', '2'): 1, ('1', '1'): 1, ('2',
'2'): 1})
Counter('122') * Counter('211')
Counter({('2', '1'): 4, ('1', '1'): 2, ('2', '2'): 2, ('1',
'2'): 1})
'''
if isinstance(other, int):
return Counter(**dict((k, v*other)
for k,v in self.items()))
elif isinstance(other, Counter):
return Counter( (x, y)
for x in self.elements()
for y in other.elements() )
else:
return NotImplemented
(Although I don't have a use case for this one).
- Paddy.
--
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Re: EXOR or symmetric difference for the Counter class
On Aug 17, 2:29 am, Raymond Hettinger pyt...@rcn.com wrote: I would like to see someone post a subclass to the ASPN Cookbook that adds a number of interesting, though not common operations. Your symmetric_difference() method could be one. A dot_product() operation could be another. Elementwise arithmetic is another option (we already have add and subtract, but could possibly use multiply, divide, etc). Scaling operations are another possibility (multiple all elements by five, for example). Raymond Sample code is at http://code.activestate.com/recipes/577362-extension-to-python-3-counter-class/ -- http://mail.python.org/mailman/listinfo/python-list
Re: EXOR or symmetric difference for the Counter class
On 14 Aug, 18:14, Raymond Hettinger pyt...@rcn.com wrote:
On Aug 12, 1:20 pm, Paddy paddy3...@googlemail.com wrote:
I find myself needing to calculate the difference between two Counters
or multisets or bags.
I want those items that are unique to each bag.
Tell us about your use cases. I'm curious how a program would ascribe
semantic meaning to the result. The phrase unique to each bag
doesn't quite cover it, perhaps something like number in either
source above the minimum held in common.
AFAICT, I've never needed something like this as a primitive. Even
the xor operation for regular sets is rarely used.
I know how to
calculate it:
b = Counter(a=1, b=2)
c = Counter(a=3, b=1)
diff = (b - c) + (c - b)
diff
Counter({'a': 2, 'b': 1})
That seems simple enough.
You could also use:
diff = (b | c) - (b c) # max(b,c) - min(b,c)
Raymond
Hi Raymond and others,
Lets say you have two *sets* of integers representing two near-copies
of some system, then a measure of their difference could be calculated
as:
len(X.symmetric_difference(Y)) / (len(X) + len(Y)) * 100 %
If the two collections of integers are allowed duplicates then you
need a Counter/bag/multi-set type and the diff calculation I gave
originally.
Thanks.
--
http://mail.python.org/mailman/listinfo/python-list
Re: EXOR or symmetric difference for the Counter class
On Aug 13, 6:36 am, Steven D'Aprano st...@remove-this-
cybersource.com.au wrote:
On Thu, 12 Aug 2010 13:20:19 -0700, Paddy wrote:
I find myself needing to calculate the difference between two Counters
or multisets or bags.
Is this collections.Counter from Python 3.1? If so, you should say so,
and if not, you should tell us which Counter class this is. It will save
people (by which I mean *me*) from spending an unrewarding few minutes
trying to import Counter in Python 2.5 and writing up a sarcastic
response ... :)
I want those items that are unique to each bag. I know how to calculate
it:
b = Counter(a=1, b=2)
c = Counter(a=3, b=1)
diff = (b - c) + (c - b)
(b - c)
Counter({'b': 1})
(c - b)
Counter({'a': 2})
diff
Counter({'a': 2, 'b': 1})
But thought why doesn't this operation appear already as a method of the
class?
Don't know. Perhaps you should put in a feature request.
--
Steven
Yes it is Counter in both 3.1 and 2.7 (And somewhere on Activestate
too).
Before I put in a feature request, I wanted to know if other have seen
the need.
--
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EXOR or symmetric difference for the Counter class
I find myself needing to calculate the difference between two Counters
or multisets or bags.
I want those items that are unique to each bag. I know how to
calculate it:
b = Counter(a=1, b=2)
c = Counter(a=3, b=1)
diff = (b - c) + (c - b)
(b - c)
Counter({'b': 1})
(c - b)
Counter({'a': 2})
diff
Counter({'a': 2, 'b': 1})
But thought why doesn't this operation appear already as a method of
the class?
- Paddy.
--
http://mail.python.org/mailman/listinfo/python-list
Accessing a method from within its own code
Hi, I was wondering if there was a shorthand way to get a reference to a method object from within that method's code. Take this code snippet as an example: import re class MyClass(object): def find_line(self, lines): if not hasattr(MyClass.do_work, matcher): MyClass.do_work.matcher = re.compile(\d - (.+)) for line in lines: m = MyClass.do_work.matcher.match(line) if m: return m.groups() Here, I have a method which uses a regular expression object to find matches. I want the regexp object to be tied to the function, but I don't want to have to recreate it every time the function is called (I am aware that regexp objects are cached, avoiding this problem, but I'm just using this as an example for what I want to know), so I've added it to the method object as an attribute and create it only if it doesn't exist. However, typing out Classname.MethodName.variablename everytime is pretty long and susceptible to refactoring issues, so I was wondering if there was a way in Python that I am missing which allows you to reference the method that the code is in (like __module__ gives a reference to the parent module). Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing a method from within its own code
I suspect that the inspection module has your answer, but that it'll be bulkier, and much slower than just doing what you're doing already. Hmm. Yeah, it does appear to be bulky. I don't think it's really any more use than what I'm doing already. Why not use the default arguments gimmick? Since this cached item is to have a module lifetime, it'd be desirable to create it when the method is being defined, which is exactly what default arguments do. I've a few different ways of emulating static function variables from C/Java and the function/method attribute one is easily the one that appeals most to my sensibilities. I find the default arguments gimmick to be a gimmick. It's co-opting a piece of functionality for something it doesn't seem like it was originally intended for and as a consequence is less readable (to my eyes). The only problem with the function/method way is that it gets rather verbose when you are dealing with a user-defined method and have to give the class name and method name and it's also a bit of a pain for moving code around when refactoring. You ever wish there was more to python scoping than just locals(), globals() and __builtins__? Like a method's class's scope too? That's where I am at with this. -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Rosetta Code: request for help
Hi, If you like programming problems and reading about/creating solutions to tasks in many languages not just Python, then take a look at Rosetta Code: http://www.rosettacode.org . If you 'lurk' for a while and read the submissions of others to get a feal for the site, then their is a list of tasks that still have no Python solution posted here: http://www.rosettacode.org/wiki/Tasks_not_implemented_in_Python that you might help out with. Some problems might need the use of specific but well known libraries such as PIL for the graphics, or specific knowledge. Others might be straight forward; or could do with an example translated to Python 3.x if it would change a lot from 2.x etc. Please take a look, I know I know I enjoy being involved. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: sorted() erraticly fails to sort string numbers
2009/4/30 Lie Ryan lie.1...@gmail.com container[:] = sorted(container, key=getkey) is equivalent to: container.sort(key=getkey) Equivalent, and in fact better since the sorting is done in-place instead of creating a new list, then overwriting the old one. Not when, as pointed out by uuid, container is not list-like (at least as far as the sort() method goes). :) Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Reading an exact number of characters from input
Hi, How would I use python to simply read a specific number of characters from standard input? raw_input() only returns when the user inputs a new line (or some other special character). I tried import sys sys.stdin.read(15) and that *returns* up to 15 characters, but it keeps accepting input (and doesn't return) until I press Enter. My initial thoughts are that a function like C's fgetc would be the easiest way to do it, but I haven't been able to find an equivalent in my google search, so I was wondering if anyone here might have some ideas. What say you? Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Introducing Python to others
Hi, As our resident python advocate, I've been asked by my team leader to give a bit of a presentation as an introduction to python to the rest of our department. It'll be less than an hour, with time for taking questions at the end. There's not going to be a whole lot of structure to it. First, I'm going to open up a python terminal and show them how the interpreter works and a few basic syntax things and then a file .py files (got to show them that python's indenting structure is not something to be afraid of :P). I think I'll mostly show things in the order that they appear in the python tutorial (http://docs.python.org/tutorial/). My question to you, dear python-list, is what suggestions do you have for aspects of python that I should show them to make them maybe think that python is better than what they are using at the moment. All of the audience will be experienced (4+ years) programmers, almost all of them are PHP developers (2 others, plus myself, work in C, know C#, perl, java, etc.). Because of this, I was thinking of making sure I included exceptions and handling, the richness of the python library and a pointing out how many modules there were out there to do almost anything one could think of. Anything else you think could make PHP developers starting think that python is a better choice? If I were to do a (very) short demonstration one web framework for the PHP devs, what should I use? CherryPy (seems to be the easiest), Django (seems to be the biggest/most used), or something else? Any other suggestions for a possible wow reaction from an audience like that? Thanks, Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: Introducing Python to others
Thanks for all your replies. A lot of very strong answers :) 2009/3/26 Mensanator mensana...@aol.com: What would you have to do to make this work? x+x+x # expecting [3,6] [2, 4, 1, 2] What's happening is that the call to map() is returning a list object. So after it calculates the first x+x, you are left with the equivalent of: [6, 6] + x Because the list object is on the left, it's __add__() function is called, which appends x to [6,6]. Instead, convert the list returned by map to a Vector before returning it. Like so: class Vector(list): ... def __add__(self, other): ... return Vector(map(add, self, other)) ... x = Vector([3,3]) x+x+x [9, 9] -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Is their an expression to create a class?
We the def statement and the lambda expression. We have the class statement, but is their an expression to create a class? Or: def F(): pass type(F) type 'function' # Is to: F2 = lambda : none type(F2) type 'function' # As class O(object): pass type(O) type 'type' # is to: # Thanks. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Is their an expression to create a class?
Chris Rebert wrote:
On Tue, Mar 17, 2009 at 2:24 PM, Robert Kern robert.k...@gmail.com wrote:
On 2009-03-17 16:13, Paddy wrote:
We the def statement and the lambda expression. We have the class
statement, but is their an expression to create a class?
Or:
def F(): pass
type(F)
type 'function'
# Is to:
F2 = lambda : none
type(F2)
type 'function'
# As
class O(object): pass
type(O)
type 'type'
# is to:
#
type('O', (object,), {})
Further detail from the docs (http://docs.python.org/library/functions.html):
type(name, bases, dict)
Return a new type object. This is essentially a dynamic form of
the class statement. The name string is the class name and becomes the
__name__ attribute; the bases tuple itemizes the base classes and
becomes the __bases__ attribute; and the dict dictionary is the
namespace containing definitions for class body and becomes the
__dict__ attribute. For example, the following two statements create
identical type objects:
class X(object):
... a = 1
...
X = type('X', (object,), dict(a=1))
New in version 2.2.
Cheers,
Chris
Thanks guys. Youve put my mind at rest!
- Paddy.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Run a python script as an exe and run a new process from it
2009/2/27 venutaurus...@gmail.com venutaurus...@gmail.com: Thanks for the reply,, I am trying to use the above application using psexec()in command line.But it failed returning the error message exited with error code 255. But when I ran the application normally it worked fine.Do I need to add anything to my python script(either the main one or the script which is calling it) to make it work. I don't have any experience with psexec, so I'm not sure if I can help you with that. I assume this means that you are trying to run the script on a remote computer? (Elsewise, why use psexec?) I took a look at it though and it seems that it always exits with *some* error code. I think it's more usual for that error code to be zero, though (it does when I run it on my machine). You might try psexec start script1.py, which might work if you've successfully set Explorer to run .py files with python.exe when you double-click on them. psexec python script1.py will work if the python.exe is in the correct path. You can also specify the full path to your python.exe. if you know it e.g.: psexec C:\python25\python.exe script1.py -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: Run a python script as an exe and run a new process from it
Try this as an outline: script1.py from subprocess import Popen if __name__ == '__main__': scriptname = script2.py Popen(python %s % scriptname, shell=True) print I'm done script2.py from time import sleep if __name__ == '__main__': while (True): print waiting.. sleep(2) ### If you install python using the Windows Installer (.exe), it should set up .py files to be opened by python when double-clicking on them. Alternatively, you can right-click on your .py file and go to Open With... then choose program, then click Browse..., you can Browse to the python executable, so Explorer will use it to open .py files when you double-click on them. As someone else mentioned there is also a py2exe program. Google it. 2009/2/26 venutaurus...@gmail.com venutaurus...@gmail.com: Hello all, I've a strange requirement where I need to run a python script just as we run an exe (by double clicking through windows explorer or by typing the script name at command prompt). In that process I should be able to execute another python script in such a way that, the second script should continue running but the main one should terminate without effecting the second one. My requirement may be little confusing so please get back if you didn't understand what I meant above. Thank you, Venu. -- http://mail.python.org/mailman/listinfo/python-list -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: Byte type?
2009/2/24 John Nagle na...@animats.com: Martin v. Löwis wrote: Please don't call something dumb that you don't fully understand. It's offenses the people who have spent lots of time developing Python -- personal, unpaid and voluntary time! Some of the people involved are on Google's payroll. Uh, what does that have to do with anything? It would only be relevant if you are saying that Google is paying them to do the work (so not just on their payroll). More importantly, it's also only relevant if ALL the people contributing are being paid by Google to do the work, which I'm pretty sure is not the case. There are people are spending lots of personal, unpaid and voluntary time developing Python. Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: How do I declare global vars or class vars in Python ?
2009/2/20 Bruno Desthuilliers bruno.42.desthuilli...@websiteburo.invalid: Note that while you *can* do direct access to the implementation attribute (here, '_A' for property 'A'), you don't *need* to so (and usually shouldn't - unless you have a very compelling reason). Interesting. Why shouldn't you? I haven't used the property() function before and probably have no call to, but when you say usually shouldn't, what is there against it? -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: How do I declare global vars or class vars in Python ?
2009/2/20 Bruno Desthuilliers bruno.42.desthuilli...@websiteburo.invalid: Interesting. Why shouldn't you? I haven't used the property() function s/function/object/ Nice try, but what I wrote was what I intended to say: http://docs.python.org/library/functions.html#property For all I know I could have used property objects several times in modules :) The case is that the whole point of using a computed attribute is to perform some computation on the value. IOW, except for a couple corner cases, only the accessors should directly access the implementation(s) attributes(s). And of course, like for any other GoldenRule(tm), it's not meant to be blindly followed. It's just that most of the times, going thru the accessors is really what you want - even from within the class code. Hmm, it doesn't seem to me like it's much of a big deal, for it to described as anything like a GoldenRule or to advise against its overuse. You use it when its appropriate and don't use it when you it's not, like any other feature. Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: How do I declare global vars or class vars in Python ?
2009/2/20 Bruno Desthuilliers bruno.42.desthuilli...@websiteburo.invalid: Check by yourself: import inspect inspect.isfunction(property) False Using this, every single builtin function returns False. That's a pretty limited definition to be being pedantic over, especially when they are in the Built-in Functions section of the manual. property() property object at 0xb7cbc144 I never said that calling it didn't return a property object :) property type 'property' So it's a type. I think I didn't make such a bad error on my part. My intent in what I was saying was to indicate that I hadn't created a property type. It's fair enough to consider type constructors as functions given how they are listed as such by the python documentation. I don't think that your correction was much help, unless you just want to say that everything is an object. Maybe you'd be right, but it's not much use to use the term that way, imo shrug dir(property) ['__class__', '__delattr__', '__delete__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__set__', '__setattr__', '__str__', 'fdel', 'fget', 'fset'] Doesn't prove a whole lot. So types have attributes... So do functions: def myfunc(): ... pass ... dir(myfunc) ['__call__', '__class__', '__delattr__', '__dict__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__module__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'func_closure', 'func_code', 'func_defaults', 'func_dict', 'func_doc', 'func_globals', 'func_name'] Hmm, it doesn't seem to me like it's much of a big deal, for it to described as anything like a GoldenRule One could say the same for each and any of the usual GoldenRules(tm). Not really. To do so would be over-generalising and not useful to discussion I guess it's your pedantry that I'm questioning. Something like don't use goto's works as a GoldenRule because it's been observed that without it, people start using goto statements in places where it's not really appropriate. When you said that [you] usually shouldn't [use properties] - unless you have a very compelling reason, your tone implied that properties are easy to misuse and tend to be. Not being familiar with properties and seeing them as being pretty harmless, I was intrigued by this, which is why I asked for an explanation. Your explanation seems to show that your tone was likely to be more personal bias than any real issue with properties. Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: How do I declare global vars or class vars in Python ?
Use the global statement. http://docs.python.org/reference/simple_stmts.html#the-global-statement A working example based on your pseudocode would be: def getA(): global A return A def getB(): global B return B def setA(value): global A A = value def setB(value): global B B = value def main(): setA(5) setB(6) print getA() print getB() if __name__ == '__main__': main() # Although honestly, I think you'd be best not coding like that (with gets and sets and all) in python. Paddy 2009/2/17 Linuxguy123 linuxguy...@gmail.com: How do I do this in Python ? # declare A,B function getA return A function getB return B function setA(value) A = value function setB(value) B = value main() getA getB dosomething setA(aValue) setB(aValue) The part I don't know to do is declare the variables, either as globals or as vars in a class. How is this done in Python without setting them to a value ? Thanks -- http://mail.python.org/mailman/listinfo/python-list -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: How do I declare global vars or class vars in Python ?
2009/2/17 MRAB goo...@mrabarnett.plus.com: It isn't possible to have an uninitialised variable. If it doesn't have a value then it doesn't exist. True, but you can use the global statement to refer to the variable within a function and read from the variable there, without it being already initialised in the module. Of course, if you try to call that function before the global has been initialised, python will complain [and rightly so :)] Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: Pythonic way to determine if a string is a number
2009/2/16 Python Nutter pythonnut...@gmail.com: silly me, forgot to mention build a set from digits + '.' and use that for testing. Cheers, PN 2009/2/16 Python Nutter pythonnut...@gmail.com: Type casting seems to be the wrong way to go about this. teststring = '15719' teststring.isdigit() returns True That takes care of integers. from string import digits digits '0123456789' now you have all the digits and you can do set testing in your logic to see if the teststring has anything in digits A dumb way to test is alphanumeric teststring2 = '105.22' teststring2.isalnum() returns True now you can go on from there and test to further to eliminate 'abcd385laf8' which on alnum() also returns true. Hmmm, this doesn't seem right to me. Unless I'm missing something, won't your code think that 123.123.123 is numeric? What about scientific or engineering notation with exponents? What's wrong with using python's own casting rules (given that you are trying to emulate the way python behaves? Or, alternatively, using a regular expression (as Nick Craig-Wood did). Given these solutions, type-conversion and catching the ValueError appears, to me, to be correct, the most concise, and the most readable solution. Of course, if you want to use your own set of rules for number encoding, then building your own regular expression would seem to be the right way to go. Paddy -- Ray, when someone asks you if you're a god, you say YES! -- http://mail.python.org/mailman/listinfo/python-list
Re: Will multithreading make python less popular?
On Feb 16, 9:34 am, rushen...@gmail.com wrote: Hi everybody, I am an engineer. I am trying to improve my software development abilities. I have started programming with ruby. I like it very much but i want to add something more. According to my previous research i have designed a learning path for myself. It's like something below. 1. Ruby (Mastering as much as possible) 2. Python (Mastering as much as possible) 3. Basic C++ or Basic Java And the story begins here. As i search on the net, I have found that because of the natural characteristics of python such as GIL, we are not able to write multi threaded programs. You are likely to find a lot of 'tick-list' type of comparison data on the web that either needs a lot of knowledge to interpret, or is misleading/wrong or all three! Their are several versions of Python out their such as Ironpython, Stackless Python, Jython as well as CPython - the main Python release. They have different threading capabilities, but compilers of feature comparison tick-lists tend to just stick to what CPython can do. As an aside; if you were thinking of using threading for performance reasons, then its best to first think of improving your general ability to explore different algorithms. A change to an algorithm often has the most impact on the performance of code. A better single threaded, single process algorithm can offer better performaance than throwing threadds or multiple processes alone when using a poor underlying algorithm. I was just exploring different ways of solving a problem on my blog: http://paddy3118.blogspot.com/2009/02/comparison-of-python-solutions-to.html (But no parallel solutions were attempted). Have fun programming! - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Pythonic way to determine if a string is a number
On Feb 15, 5:46 pm, pyt...@bdurham.com wrote: What's the Pythonic way to determine if a string is a number? By number I mean a valid integer or float. I searched the string and cMath libraries for a similar function without success. I can think of at least 3 or 4 ways to build my own function. Here's what I came up with as a proof-of-concept. Are there 'better' ways to perform this type of test? Thanks, Malcolm code def isnumber( input ): try: if '.' in input: num = float( input ) else: num = int( input ) return True except ValueError: return False if __name__ == '__main__': tests = 12 -12 -12.34 .0 . 1 2 3 1 . 2 just text for test in tests.split( '\n' ): print 'test (%0s), isnumber: %1s' % \ ( test.strip(), isnumber( test ) ) /code Their is a good answer given on Rosetta Code here: http://www.rosettacode.org/wiki/IsNumeric#Python - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Python Fractions issue.
(From: http://paddy3118.blogspot.com/2008/09/python-fractions-issue.html) There seems to be a problem/difference in calculating with the new fractions module when comparing Python 26rc2 and 30rc1 I was reading the paper Interval Arithmetic: Python Implementation and Applications and thought to try the first example function f(x,y), which needs more precision than Python floating point provides (on my Windows PC), to calculate a sensible answer. Ahah, I thought, lets try this with Fractions - so I first installed Python 30rc1, typed in the Function - saw the rubbish result, then used Fractions and got the 'right' result. I then wondered if fractions had been back-ported to Python 2.6rc2, found that it had, but got different results. As you can see from the table, Python 2.6rc2 has a problem calculating t3 = F(11,2) * y**8 + x/(2*y), where F is Fraction. I wonder where the problem lies? (For the Table, please see the blog entry). - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: ctypes: loading .so file on Linux
On Aug 23, 2:33 pm, Paddy [EMAIL PROTECTED] wrote: Hi, I am am falling at the first hurdle when trying to access a library using ctypes. I have a file libucdb.so which the file command says is shared object, but I cannot get it to load: Any help would be appreciated: dmccarthy: file /opt/questasim_6.4/questasim/linux/libucdb.a /opt/ questasim_= 6.4/questasim/linux/libucdb.so /opt/questasim_6.4/questasim/linux/libucdb.a: current ar archive /opt/questasim_6.4/questasim/linux/libucdb.so: ELF 32-bit LSB shared object,= Intel 80386, version 1 (SYSV), not stripped dmccarthy: python ActivePython 2.5.1.1 (ActiveState Software Inc.) based on Python 2.5.1 (r251:54863, May 2 2007, 08:46:07) [GCC 3.3.4 (pre 3.3.5 20040809)] on linux2 Type help, copyright, credits or license for more information. cdll.LoadLibrary(libc.so.6) Traceback (most recent call last): File stdin, line 1, in module NameError: name 'cdll' is not defined from ctypes import * ^[[A^[[A ^e stdin, line 1 SyntaxError: invalid syntax cdll.LoadLibrary(libc.so.6) CDLL 'libc.so.6', handle 2a958a2900 at 2a95dda490 cdll.LoadLibrary(libucdb.so) Traceback (most recent call last): File stdin, line 1, in module File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 423, in LoadLibrary return self._dlltype(name) File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 340, in __init__ self._handle =3D _dlopen(self._name, mode) OSError: libucdb.so: cannot open shared object file: No such file or directo= ry cdll.LoadLibrary(libc.so.6) CDLL 'libc.so.6', handle 2a958a2900 at 2a95df3ad0 libc =3D CDLL(libc.so.6) libc CDLL 'libc.so.6', handle 2a958a2900 at 2a95dda490 libc =3D CDLL(libucdb.so) Traceback (most recent call last): File stdin, line 1, in module File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 340, in __init__ self._handle =3D _dlopen(self._name, mode) OSError: libucdb.so: cannot open shared object file: No such file or directo= ry libc =3D CDLL(/opt/questasim_6.4/questasim/linux/libucdb.so) Traceback (most recent call last): File stdin, line 1, in module File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 340, in __init__ self._handle =3D _dlopen(self._name, mode) OSError: /opt/questasim_6.4/questasim/linux/libucdb.so: cannot open shared o= bject file: No such file or directory ^[[A File stdin, line 1 ^ SyntaxError: invalid syntax - Paddy. Any help would be appreciated. Thanks. -- http://mail.python.org/mailman/listinfo/python-list
Re: Psyco == tracing optimization?
On Aug 24, 8:11 am, Fredrik Lundh [EMAIL PROTECTED] wrote: Banibrata Dutta wrote: AFAIK, the same logic used in runtime optimization of several other dynamic languages or shell-scripting languages (including Perl), for quite a while. Trace trees are widely used? Got any references for that? /F I too feel that if Perl had such optimizations as Psyco gives Python then they would shout about it. I wonder about the new term and if it fits in the same 'box' as what Psyco does, for example, who was aware of whose work? - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Regex on a huge text
On Aug 22, 9:19 pm, Medardo Rodriguez [EMAIL PROTECTED] wrote: On Fri, Aug 22, 2008 at 11:24 AM, Dan [EMAIL PROTECTED] wrote: I'm looking on how to apply a regex on a pretty huge input text (a file that's a couple of gigabytes). I found finditer which would return results iteratively which is good but it looks like I still need to send a string which would be bigger than my RAM. Is there a way to apply a regex directly on a file? Any help would be appreciated. You can call *grep* posix utility. But if the regex's matches are possible only inner the context of a line of that file: #code res = [] with file(filename) as f: for line in f: res.extend(getmatches(regex, line)) # Of course getmatches describes the concept. #/code Regards Try and pre-filter your file on a line basis to cut it down , then apply a further filter on the result. For example, if you were looking for consecutive SPAM records with the same Name field then you might first extract only the SPAM records from the gigabytes to leave something more manageable to search for consecutive Name fields in. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
ctypes: loading .so file on Linux
Hi, I am am falling at the first hurdle when trying to access a library using ctypes. I have a file libucdb.so which the file command says is shared object, but I cannot get it to load: Any help would be appreciated: dmccarthy: file /opt/questasim_6.4/questasim/linux/libucdb.a /opt/ questasim_= 6.4/questasim/linux/libucdb.so /opt/questasim_6.4/questasim/linux/libucdb.a: current ar archive /opt/questasim_6.4/questasim/linux/libucdb.so: ELF 32-bit LSB shared object,= Intel 80386, version 1 (SYSV), not stripped dmccarthy: python ActivePython 2.5.1.1 (ActiveState Software Inc.) based on Python 2.5.1 (r251:54863, May 2 2007, 08:46:07) [GCC 3.3.4 (pre 3.3.5 20040809)] on linux2 Type help, copyright, credits or license for more information. cdll.LoadLibrary(libc.so.6) Traceback (most recent call last): File stdin, line 1, in module NameError: name 'cdll' is not defined from ctypes import * ^[[A^[[A ^e stdin, line 1 SyntaxError: invalid syntax cdll.LoadLibrary(libc.so.6) CDLL 'libc.so.6', handle 2a958a2900 at 2a95dda490 cdll.LoadLibrary(libucdb.so) Traceback (most recent call last): File stdin, line 1, in module File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 423, in LoadLibrary return self._dlltype(name) File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 340, in __init__ self._handle =3D _dlopen(self._name, mode) OSError: libucdb.so: cannot open shared object file: No such file or directo= ry cdll.LoadLibrary(libc.so.6) CDLL 'libc.so.6', handle 2a958a2900 at 2a95df3ad0 libc =3D CDLL(libc.so.6) libc CDLL 'libc.so.6', handle 2a958a2900 at 2a95dda490 libc =3D CDLL(libucdb.so) Traceback (most recent call last): File stdin, line 1, in module File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 340, in __init__ self._handle =3D _dlopen(self._name, mode) OSError: libucdb.so: cannot open shared object file: No such file or directo= ry libc =3D CDLL(/opt/questasim_6.4/questasim/linux/libucdb.so) Traceback (most recent call last): File stdin, line 1, in module File /software/unix-soft/linux/ActivePython-2.5.1.1-linux-x86_64/ lib/pyth= on2.5/ctypes/__init__.py, line 340, in __init__ self._handle =3D _dlopen(self._name, mode) OSError: /opt/questasim_6.4/questasim/linux/libucdb.so: cannot open shared o= bject file: No such file or directory ^[[A File stdin, line 1 ^ SyntaxError: invalid syntax - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Psyco == tracing optimization?
Just wondered if this: http://arstechnica.com/news.ars/post/20080822-firefox-to-get-massive-javascript-performance-boost.html, is a new name for what is done by Psyco? - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Should Python raise a warning for mutable default arguments?
On Aug 22, 4:55 pm, Peter Otten [EMAIL PROTECTED] wrote: [EMAIL PROTECTED] wrote: DrScheme is an implementation of Scheme that is very newbie-friendly. It has several limited sub-languages, etc. So maybe a command line option can be added to Python3 ( - newbie ? :-) ) that just switches on similar warnings, to help newbies (in schools, where there's a teacher that encourages to always use that command line option) avoid some of the most common traps. Or maybe bundle pychecker with idle? $ cat tmp.py def test(x, a=[]): a.append(x) return a for i in range(5): print test(i) $ pychecker tmp.py Processing tmp... [0] [0, 1] [0, 1, 2] [0, 1, 2, 3] [0, 1, 2, 3, 4] Warnings... tmp.py:2: Modifying parameter (a) with a default value may have unexpected consequences Though it might be interesting to ask a newbie what he expects when warned of unexpected consequences ;) Peter +1 on this. It seems an obvious think to add to a lint-like tool rather than burdening core Python. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python one-liner??
On Aug 22, 10:03 pm, Matimus [EMAIL PROTECTED] wrote: Do we have python one-liner like perl one-liner 'perl -e'?? The answer is python -c... but python -h is useful too. Matt And Python is not optimised for one-liner solutions. I have been known to construct multi-line -c arguments using the bash shell on Unix (as bash supports multi-line quotes), but creating and then deleting a temporary file saves me from 'quoting hell'. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Validation of parameters
On Aug 10, 9:13 am, Kless [EMAIL PROTECTED] wrote:
Which is the best mode for validation of parameters? I'm using the
next way but it is not well testable.
-
if not self._foo:
try:
raise ValueError('ValueError: foo not found')
except ValueError, err:
print (err.message)
print(Valid values: %s\n % self.valid_foo)
sys.exit(1)
...
...
-
If you just want the absense of _foo to raise an exception then why to
just reference self._foo and leave the hard work to ptyhon? Something
like:
self._foo
If it is present then fine, if it is not then an exception is raised.
Here it is in the Python shell:
class tmp(object):
def __init__(self):
self._foo
dummy = tmp()
Traceback (most recent call last):
File pyshell#4, line 1, in module
dummy = tmp()
File pyshell#3, line 3, in __init__
self._foo
AttributeError: 'tmp' object has no attribute '_foo'
- Paddy.
--
http://mail.python.org/mailman/listinfo/python-list
Re: What Python looks like
On Aug 4, 8:06 pm, iu2 [EMAIL PROTECTED] wrote: Hi, This is a little bit strange post, but I'm curious... I learned Python from its tutorial step by step, and practicing writing small scripts. I haven't seen a Python program before knowing Python. I'm curious, what did Python code look like to those of you who have seen a bunch of Python code for the first time before knowing Python? (I can tell, for example, that seeing perl for the first time looked like C with many $$$, I could see if and for and while but they were meaningless. Or Lisp for the first time looked like many words, no operators, how could that make a program???) Thanks Strange you should mention this. I am currently new to Rosetta Code http://www.rosettacode.org/ where some pages I have been looking at such as the page for Zig Zag, and a page I created called Spiral have had very terse solutions, and long explanations in the talk pages all written in the J language. I can read the lines between the code samples enough to intrigue , (OK frustrate), me - but the code is impenetrable. I am not sure if J attracts good programmers or if learning J forces you to think about solutions in different or useful ways. I've learnt A LISP-like language, dabbled with forth prolog constraints - maybe its time to learn J and find out if this array programming malarky will bring new insight to my problem solving - but it will never be readable :-) - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Native Code vs. Python code for modules
On Jul 30, 4:56 am, koblas [EMAIL PROTECTED] wrote: Ruby has been getting pummeled for the last year or more on the performance subject. They've been working hard at improving it. From my arm chair perspective Python is sitting on it's laurels and not taking this as seriously as it probably should. I personally DON'T think that the developers should be chasing down every micro-benchmark. Someone has to look-up and see the bigger picture. If you take a look at a larger set of micro benchmarks, then Ruby is below par when compared to Python and Perl on speed. I had the misfortune to read their development group entries when a critical bug was 'fixed' by a release from Japan that didn't have enough testing and so think the Ruby development 'group' have problems of quality that they also need to address. (And are doing I think by adding to their test-suite). PyPy and previous tools like Psyco are ways in which Python developers are continuing to see above the eternal grind of micro- optimising the C-interpreter to try and give us tools that can approach compiled language speeds from the language we love. I like to think of it as working smarter rather than harder - the brains a much better muscle :-) - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Parsing VHDL with python, where to start.
On Jul 21, 12:09 pm, Svenn Are Bjerkem [EMAIL PROTECTED] wrote: Hi, I am in the need to write an application for PyQt to visualise the structure of a VHDL project I am working on. Looking for a sensible way to parse VHDL files and putting them into a data structure that PyQt can represent as a tree (or whatever the MVC is supporting) through search engines does not give me many hints. From what I know, VHDL is not a very easy language to parse. There seems to be a parser for perl available, but I do not know if it is wise to use a perl module as a template for writing something similar in python. My initial idea is to start simple and extend features in my application, but I fear that I may start off with wrong ideas how to parse and then code myself into a dead-end requiring myself to rewrite the whole application in order to get any further. I would start finding definitions of entities and the instantiations of these and build a tree from a set of external vhdl files stored in a file hierarchy. If somebody have a starting point where to get going with a task like this, I would be happy to know. -- kind regards, Svenn Been their, partially done that. I started parsing an old version of VHDL (VHDL 87 I think); using regular expressions and carrying state around myself. It was tough, and I was doing it , but then Work mentioned that they were going to need to parse later versions of VHDL and that was a whole new ball- game, specifically configuration type information could be mixed in with the architecture. Luckily work had also decided to by in a commercial parser. I learned that add-hoc parsers have limits to their maintainability and become complex. You might not have such problems if your VHDL is all in one library. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Doubt
On Jul 23, 3:51 pm, ജഗന്നാഥ് [EMAIL PROTECTED] wrote:
Friends
I am a Perl programmer new to Python. I have a small doubt.
How to convert the perl notation
$a = ; expression in Python ?
How to represent the loop
for ($a = $b; $a=$c;$a++){
} in Python
Jagan
Linguist
This might help you generally:
http://wiki.python.org/moin/PerlPhrasebook
- Paddy.
--
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Re: software engineering foundations?
On Jul 22, 7:52 pm, [EMAIL PROTECTED] wrote: Sorry for the off-topic-ish post. My son (a fairly junior sysadmin type) mentioned to me today that he was looking for online courses for Perl. (I don't hold that against him. Perl is still a lingua franca in the sysadmin realm.) In my work I have from time-to-time had to pick up and maintain scripts (generally shell/Python stuff) which non-professional programmers have written. It's never what you would call a pleasant task. There are software construction skills which are entirely distinct from the language in which you are programming. We can tout object-oriented, structured programming, test-driven development or other software engineering techniques, but there is a body of knowledge out there which is orthogonal to the language in which the code is written. People who are not professional programmers often lack those skills and their code shows it. Are there any good online resources for this software structure axis? Googling for object oriented programming tutorial yields a bunch of stuff, much of it language-specific. I'm trying to find something a bit more general than that though. I Googled for software engineering tutorial as well. Most of the early hits were either inaccessible (ACM subscription only) or contents-like stuff (conference announcements, for example). Number eight on the list was this rather promising page: http://www.cmcrossroads.com/bradapp/links/swe-links.html It was last updated over 10 years ago. I find it hard to believe that so little has changed in that time that some other page with more recent references hasn't percolated to the top of Google's page rank! After all, the Web has grown just a tad in that timeframe. I have a sneaking suspicion that what I'm looking for is out there, but that I'm not asking Google in the right manner. Any and all pointers/suggestions cheerfully accepted. Thx, -- Skip Montanaro - [EMAIL PROTECTED] -http://www.webfast.com/~skip/ -- ELON MUSK: If fuel cells were good, don't think you'd see them somewhere, like maybe in a laptop or a cell phone or a $200 million military satellite maybe? And yet, where do you see them? SPENCER MICHELS: You don't. ELON MUSK: Exactly. Is this the kind of thing you are after? http://www.swc.scipy.org/ Software Carpentry Overview Many scientists and engineers spend much of their lives programming, but only a handful have ever been taught how to do this well. As a result, they spend their time wrestling with software, instead of doing research, but have no idea how reliable or efficient their programs are. This course is an intensive introduction to basic software development practices for scientists and engineers that can reduce the time they spend programming by 20-25%. All of the material is open source: it may be used freely by anyone for educational or commercial purposes, and research groups in academia and industry are actively encouraged to adapt it to their needs. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Bidirectional Generators
On Jul 22, 10:07 pm, william tanksley [EMAIL PROTECTED] wrote: Okay, I'm almost finished with my first bidirectional generator. By almost finished I mean both that it's almost working, and that I'm almost about to replace it with a class that works a bit more like what I currently understand. Surely some other people have worked with this feature... Are there any pages that discuss how it's been useful? No, I don't want to see an implementation of coroutines. I get that one already. :-) -Wm What's one of them then? - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Question
On Jul 19, 10:27 am, [EMAIL PROTECTED] wrote: Why is Perl so much better than python? Coz its endorsed by: Chernobble valve controls. Barings Bank. The society of the Mortgage Brokers of America. The Bush Disaster relief fund for the Southern States. And, of course, is the tool of choice when looking for weapons of mass destruction in Iraq. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: question
On Jul 20, 6:39 pm, [EMAIL PROTECTED] wrote: Nobody any sensible answers. Too complicated I suppose! The sensible question was? -- http://mail.python.org/mailman/listinfo/python-list
Re: singletons
On Jul 16, 11:20 pm, Craig Allen [EMAIL PROTECTED] wrote: Hey, forgive me for just diving in, but I have a question I was thinking of asking on another list but it really is a general question so let me ask it here. It's about how to approach making singletons. Hi Craig, This might be good for a general background on Design Patters in Python: http://uk.youtube.com/watch?v=0vJJlVBVTFg - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: read file into list of lists
On Jul 11, 2:15 pm, antar2 [EMAIL PROTECTED] wrote: Hello, I can not find out how to read a file into a list of lists. I know how to split a text into a list sentences = line.split(\n) following text for example should be considered as a list of lists (3 columns and 3 rows), so that when I make the print statement list[0] [0], that the word pear appears pear noun singular books nouns plural table noun singular Can someone help me? Thanks lofl = [line.strip().split() for line in the_opened_file] - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: read file into list of lists
On Jul 11, 9:32 pm, John Machin [EMAIL PROTECTED] wrote: On Jul 11, 11:35 pm, Paddy [EMAIL PROTECTED] wrote: On Jul 11, 2:15 pm, antar2 [EMAIL PROTECTED] wrote: Hello, I can not find out how to read a file into a list of lists. I know how to split a text into a list sentences = line.split(\n) following text for example should be considered as a list of lists (3 columns and 3 rows), so that when I make the print statement list[0] [0], that the word pear appears pear noun singular books nouns plural table noun singular Can someone help me? Thanks lofl = [line.strip().split() for line in the_opened_file] line = ' foo bar ' line.strip().split() ['foo', 'bar'] line.split() ['foo', 'bar'] Thanks , ta. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: re.search much slower then grep on some regular expressions
On Jul 5, 7:01 am, Peter Otten [EMAIL PROTECTED] wrote: Paddy wrote: It is not a smarter algorithm that is used in grep. Python RE's have more capabilities than grep RE's which need a slower, more complex algorithm. So you're saying the Python algo is alternatively gifted... Peter The following isn't the article I read on regexp types and their speed differences but it does give info on regexp engine types: http://books.google.co.uk/books?id=GX3w_18-JegCpg=PA145lpg=PA145dq=%2Bregex+%2Bspeed+%2Bgrep+%2Btcl+source=webots=PHljNqeuJZsig=CyBCOZYsyZaJTMfj2Br53if46Bchl=ensa=Xoi=book_resultresnum=3ct=result#PPA145,M1 - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: re.search much slower then grep on some regular expressions
On Jul 5, 4:13 pm, Mark Dickinson [EMAIL PROTECTED] wrote: It seems like an appropriate moment to point out *this* paper: http://swtch.com/~rsc/regexp/regexp1.html That's the one! Thanks Mark. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: re.search much slower then grep on some regular expressions
On Jul 4, 1:36 pm, Peter Otten [EMAIL PROTECTED] wrote:
Henning_Thornblad wrote:
What can be the cause of the large difference between re.search and
grep?
grep uses a smarter algorithm ;)
This script takes about 5 min to run on my computer:
#!/usr/bin/env python
import re
row=
for a in range(156000):
row+=a
print re.search('[^ =]*/',row)
While doing a simple grep:
grep '[^ =]*/' input (input contains 156.000 a in
one row)
doesn't even take a second.
Is this a bug in python?
You could call this a performance bug, but it's not common enough in real
code to get the necessary brain cycles from the core developers.
So you can either write a patch yourself or use a workaround.
re.search('[^ =]*/', row) if / in row else None
might be good enough.
Peter
It is not a smarter algorithm that is used in grep. Python RE's have
more capabilities than grep RE's which need a slower, more complex
algorithm.
You could argue that if the costly RE features are not used then maybe
simpler, faster algorithms should be automatically swapped in but
- Paddy.
--
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Re: Getting sorting order
On Jul 1, 8:26 pm, Tobiah [EMAIL PROTECTED] wrote: master,slave1,slave2=zip(*x) What does the asterisk do here? Thanks ** Posted fromhttp://www.teranews.com** Hi Tobiah, I blogged extensively on this zip(*x) trick here: http://paddy3118.blogspot.com/2007/02/unzip-un-needed-in-python.html - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting two dimentional array by column?
On Jul 2, 10:35 pm, Tobiah [EMAIL PROTECTED] wrote: Imagine an excel spreadsheet. I can choose a column and sort the records based on the items in that column. I would like to do the same thing with a large two dimensional array. What would be the fastest way (in computation time) to accomplish this? Now that I think about the problem more, I really want to sort an array of dictionaries according one of the keys of each. Could I use: array.sort(key = something) Where something looks at the proper item in the current row? I can't quite visualize how to pull the item out of the dictionary. Thanks ** Posted fromhttp://www.teranews.com** Hi Tobiah, Try this: arrayofdicts.sort( key = lambda dictinarray: dictinarray.get(sortkeyname) ) - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
[issue3214] Suggest change to glossary explanation: Duck Typing
Paddy McCarthy [EMAIL PROTECTED] added the comment: Hi Georg, A bit of relevant background about me: I've been interested in Duck Typing _specifically_ for a couple of years when I started watching edits to it on Wikipedia. I researched the history of the use of the term and changed the attribution of first use to Alex Martelli after digging in Google, and still trawl reading code and articles on the subject. But I DONT think this makes me an expert - Duck typing is a 'mould-able' term and the things we write about it help to define it. On your comment about hasattr: I think more and more that Duck-Typing is what allows us, (as in Python), to substitute one class for another in a method previously designed with only the other in mind - you know, as in the canonical example of file-like objects such as StringIO substituting in methods defined originally for files. In this case hasattr checks don't add anything, and EAFP is all important. I tried to get wider context on this by posting it originally to comp.lang.python but no one was interested. I don't normally frequent the developers forumbut maybe we should open the issue to that audience? - Paddy. ___ Python tracker [EMAIL PROTECTED] http://bugs.python.org/issue3214 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue3214] Suggest change to glossary explanation: Duck Typing
New submission from Paddy McCarthy [EMAIL PROTECTED]: The official glossary entry here: http://docs.python.org/tut/node18.html#l2h-46 says: duck-typing Pythonic programming style that determines an object's type by inspection of its method or attribute signature rather than by explicit relationship to some type object (If it looks like a duck and quacks like a duck, it must be a duck.) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type() or isinstance(). Instead, it typically employs hasattr() tests or EAFP programming. I think it is should be changed to delete the use of hasattr and just rely on EAFP as in the second example here: http://en.wikipedia.org/wiki/Python_syntax_and_semantics#Exceptions The text would then read: duck-typing Pythonic programming style that determines an object's type by inspection of its method or attribute signature rather than by explicit relationship to some type object (If it looks like a duck and quacks like a duck, it must be a duck.) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type(), hasattr() or isinstance(). Instead, it typically employs an EAFP style of programming. The reason is that a hasattr test only tests for an attribute name. If it is present and say the method signature is wrong, then its the excecution of the code using the attribute that will find that out so it is redundant. Best to use EAFP for Duck typing as we trust you know what it is you are doing. - Paddy. -- assignee: georg.brandl components: Documentation messages: 68815 nosy: georg.brandl, paddy3118 severity: normal status: open title: Suggest change to glossary explanation: Duck Typing type: feature request versions: Python 2.5, Python 2.6, Python 3.0 ___ Python tracker [EMAIL PROTECTED] http://bugs.python.org/issue3214 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Propose slight change to tutorial glossary entry on Duck Typing
The official glossary entry here: http://docs.python.org/tut/node18.html#l2h-46 says: duck-typing Pythonic programming style that determines an object's type by inspection of its method or attribute signature rather than by explicit relationship to some type object (If it looks like a duck and quacks like a duck, it must be a duck.) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type() or isinstance(). Instead, it typically employs hasattr() tests or EAFP programming. I think it is should be changed to delete the use of hasattr and just rely on EAFP as in the second example here: http://en.wikipedia.org/wiki/Python_syntax_and_semantics#Exceptions The text would then read: duck-typing Pythonic programming style that determines an object's type by inspection of its method or attribute signature rather than by explicit relationship to some type object (If it looks like a duck and quacks like a duck, it must be a duck.) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using type(), hasattr() or isinstance(). Instead, it typically employs an EAFP style of programming. The reason is that a hasattr test only tests for an attribute name. If it is present and say the method signature is wrong, then its the excecution of the code using the attribute that will find that out so it is redundant. Best to use EAFP for Duck typing as we trust you know what it is you are doing. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Question: How do I format printing in python
Lie wrote:
On Jun 24, 12:12 am, [EMAIL PROTECTED] wrote:
Hi All,
How do I format printed data in python?
I could not find this in the Python Reference
Manual:http://docs.python.org/ref/print.html
Nor could I find it in Matloff's great
tutorial:http://heather.cs.ucdavis.edu/~matloff/Python/PythonIntro.pdf
For example, how do I turn this:
512 Jun 5 2004 X11r6
22 Jan 17 2005 a2p
22 Jan 17 2005 acctcom
5374 Sep 15 2002 acledit
5664 May 13 2004 aclget
12020 May 13 2004 aclput
115734 Jun 2 2004 adb
46518 Jun 4 2004 admin
66750 Sep 16 2002 ali
1453 Sep 15 2002 alias
28150 Jun 4 2004 alog
15 May 12 2005 alstat
into this:
512Jun 5 2004X11r6
22 Jan 17 2005a2p
22 Jan 17 2005acctcom
5374 Sep 15 2002acledit
5664 May 13 2004aclget
12020 May 13 2004aclput
115734 Jun 2 2004adb
46518 Jun 4 2004admin
66750 Sep 16 2002ali
1453 Sep 15 2002alias
28150 Jun 4 2004alog
15 May 12 2005alstat
Thank you
There is string formatting
print formatspecifier_string % data_sequence
The format specifier is similar to the one used in C's printf, and
data sequence may be tuple or list. Dictionary may also be used for
data, but it has its own way to specify string formatting since
dictionary is unordered but indexed by the dict key.
I have attached a prog I wrote to answer someones elses similar problem.
- Paddy.
from StringIO import StringIO
from pprint import pprint as pp
left_justified = False
debug = False
textinfile = '''I$created$a$solution$for$a$program$I$am$writing$that
makes$columns$line$up$when$outputted$to$the$command
line.$I$am$new$to$Python,$and$am$hoping$I$might$get
some$input$on$this$topic.$In$the$text$file$that$the
program$reads,$the$fields$(columns)$are$delimited$by
'dollar'$and$the$records$(lines)$are$delimited$by
newlines$'\\n'.$So$one$line$looks$like:$'''
Solution to problem posed at:
http://www.kbrandt.com/2008/06/getting-command-line-output-columns-to.html
Output is the following if left-justified:
# Column-aligned output:
Icreated asolution for a program Iam
writing that
makescolumns line up when outputted tothe command
line.I am new toPython, and am hoping I
might get
some input on this topic.Inthe text filethat
the
program reads, the fields (columns) are delimited by
'dollar' and the records (lines) are delimited by
newlines '\n'. So one line looks like:
And like this if not left-justified:
# Column-aligned output:
I createda solution for a programI am
writing that
makes columns line up when outputtedto the command
line. I am newto Python, and am hoping
I might get
some input on thistopic.In the textfile
that the
program reads, the fields (columns) are delimited by
'dollar' and the records (lines) are delimited by
newlines '\n'. So one line looks like:
infile = StringIO(textinfile)
fieldsbyrecord= [line.strip().split('$') for line in infile]
if debug: print fieldsbyrecord:; print (fieldsbyrecord)
# pad to same number of fields per record
maxfields = max(len(record) for record in fieldsbyrecord)
fieldsbyrecord = [fields + ['']*(maxfields - len(fields))
for fields in fieldsbyrecord]
if debug: print padded fieldsbyrecord:; print (fieldsbyrecord)
# rotate
fieldsbycolumn = zip(*fieldsbyrecord)
if debug: print fieldsbycolumn:; print (fieldsbycolumn)
# calculate max fieldwidth per column
colwidths = [max(len(field) for field in column)
for column in fieldsbycolumn]
if debug: print colwidths:; print (colwidths)
# pad fields in columns to colwidth with spaces
# (Use -width for left justification,)
fieldsbycolumn = [ [%*s % (-width if left_justified else width, field) for
field in column]
for width, column in zip(colwidths, fieldsbycolumn) ]
if debug: print padded fieldsbycolumn:; print (fieldsbycolumn)
# rotate again
fieldsbyrecord = zip(*fieldsbycolumn)
if debug: print padded rows and fields, fieldsbyrecord:; print
(fieldsbyrecord)
# printit
print \n# Column-aligned output:
for record in fieldsbyrecord:
print .join(record)
--
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Re: Is there any way to find out sizeof an object
On Jun 24, 6:00 am, srinivasan srinivas [EMAIL PROTECTED] wrote: Hi, I have written a class which has some attributes. I want to know how do i find out the size of an instance of this class?? class T(object): def __init__(self, fn_name, *args, **kwds): self.fn_name = fn_name self.args = args self.kwds = kwds Thanks, Srini Bollywood, fun, friendship, sports and more. You name it, we have it onhttp://in.promos.yahoo.com/groups/bestofyahoo/ Check memory Create a million Check memory Do maths! ;-) - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Ruby doctest
I monitor changes to the Wikipedia doctest page, and so noticed a change in the Ruby implementation of doctest. Scooting around their implementation I found that they have an !!! special directive that says drop into the interpreter at this point when testing allowing debugging in context. http://github.com/tablatom/rubydoctest/wikis/special-directives - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: ISO dict = xml converter
On Jun 20, 1:37 pm, kj [EMAIL PROTECTED] wrote:
Hi. Does anyone know of a module that will take a suitable Python
dictionary and return the corresponding XML structure?
In Perl I use XML::Simple's handy XMLout function:
use XML::Simple 'XMLout';
my %h = ( 'Foo' = +{
'Bar' = +{
'Baz' = [ { 'meenie' = 3 },
{ 'meenie' = 7 } ],
'eenie' = 4,
},
'minie' = 1,
'moe' = 2,
} );
print XMLout( \%h, KeepRoot = 1, KeyAttr = undef );
__END__
Foo minie=1 moe=2
Bar eenie=4
Baz meenie=3 /
Baz meenie=7 /
/Bar
/Foo
Is there a Python module that can do a similar conversion from
a Python dict to an XML string?
(FWIW, I'm familiar with xml.marshal.generic.dumps, but it does
not produce an output anywhere similar to the one illustrated
above.)
TIA!
Kynn
--
NOTE: In my address everything before the first period is backwards;
and the last period, and everything after it, should be discarded.
Try:
http://pyxml.sourceforge.net/topics/howto/node26.html
- Paddy.
--
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Re: Pattern Matching Over Python Lists
On Jun 20, 1:44 am, Chris [EMAIL PROTECTED] wrote: Thanks for your help. Those weren't quite what I was looking for, but I ended up figuring it out on my own. Turns out you can actually search nested Python lists using simple regular expressions. Strange? How do you match nested '[' ... ']' brackets? - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Mapping None. Why?
On Jun 13, 12:49 pm, David C. Ullrich [EMAIL PROTECTED] wrote: On Thu, 12 Jun 2008 12:05:02 -0700 (PDT), Paddy [EMAIL PROTECTED] wrote: Iam wondering why the peculiar behavior of map when the function in given as None: If you start with a value x and then apply no function at all to it, what results is x. David C. Ullrich True, but None is not a function. It's a sentinel value to turn on the functionality. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Summing a 2D list
On Jun 13, 1:12 pm, Karsten Heymann [EMAIL PROTECTED]
wrote:
Hi Mark,
Mark [EMAIL PROTECTED] writes:
I have a scenario where I have a list like this:
UserScore
1 0
1 1
1 5
2 3
2 1
3 2
4 3
4 3
4 2
And I need to add up the score for each user to get something like
this:
UserScore
1 6
2 4
3 2
4 8
Is this possible? If so, how can I do it? I've tried looping through
the arrays and not had much luck so far.
Although your problem has already been solved, I'd like to present a
different approach which can be quite a bit faster. The most common
approach seems to be using a dictionary:
summed_up={}
for user,vote in pairs:
if summed_up.has_key(user):
summed_up[user]+=vote
else:
summed_up[user]=vote
But if the list of users is compact and the maximum value is known
before, the using a list and coding the user into the list position is
much more elegant:
summed_up=list( (0,) * max_user )
for user,vote in pairs:
summed_up[user] += vote
I've run a quick and dirty test on these approaches and found that the
latter takes only half the time than the first. More precisely, with
about 2 million pairs, i got:
* dict approach: 2s
(4s with try: ... except KeyError: instead of the if)
* list approach: 0.9s
BTW this was inspired by the book Programming Pearls I read some
years ago where a similar approach saved some magnitudes of time
(using a bit field instead of a list to store reserved/free phone
numbers IIRC).
Yours,
Karsten
How does your solution fare against the defaultdict solution of:
d = collections.defaultdict(int)
for u,s in zip(users,score): d[u] += s
- Paddy
--
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Re: Counting things fast - was Re: Summing a 2D list
On Jun 12, 4:14 pm, Gerhard Häring [EMAIL PROTECTED] wrote: Aidan wrote: does this work for you? users = [1,1,1,2,2,3,4,4,4] score = [0,1,5,3,1,2,3,3,2] d = dict() for u,s in zip(users,score): if d.has_key(u): d[u] += s else: d[u] = s for key in d.keys(): print 'user: %d\nscore: %d\n' % (key,d[key]) I've recently had the very same problem and needed to optimize for the best solution. I've tried quite a few, including: 1) using a dictionary with a default value d = collections.defaultdict(lambda: 0) d[key] += value SNIP -- Gerhard This might be faster, by avoiding the lambda: d = collections.defaultdict(int) d[key] += value - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Mapping None. Why?
Iam wondering why the peculiar behavior of map when the function in
given as None:
Help on built-in function map in module __builtin__:
map(...)
map(function, sequence[, sequence, ...]) - list
Return a list of the results of applying the function to the items
of
the argument sequence(s). If more than one sequence is given, the
function is called with an argument list consisting of the
corresponding
item of each sequence, substituting None for missing values when
not all
sequences have the same length. If the function is None, return a
list of
the items of the sequence (or a list of tuples if more than one
sequence).
It seems as the action whith none is the same as using a function of
lambda *x: x
As in the following example:
l1 = 'asdf'
l2 = 'qwertyuip'
l3 = range(3)
l1,l2,l3
('asdf', 'qwertyuip', [0, 1, 2])
map(lambda *x: x, l1,l2,l3) == map(None, l1,l2,l3)
True
On looking up map on Wikipedia there is no mention of this special
behaviour,
So my question is why?
Thanks, Paddy.
--
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Re: Mapping None. Why?
On Jun 12, 8:55 pm, Diez B. Roggisch [EMAIL PROTECTED] wrote: And the OP's question was about map not being conforming to the definition on wikipedia - which I don't think it's not. It is not defined what map is to do with None (or NULL or nil or... ) as argument. Diez Oh no! Sorry to give that impression. I don't think that map should be like what Wikipedia says, I was just looking for another example of an implementation that might mention the behaviour. I just want to know the thoughts behind this behaviour in the Python map. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Mapping None. Why?
On Jun 12, 9:48 pm, Robert Kern [EMAIL PROTECTED] wrote: Paddy wrote: On looking up map on Wikipedia there is no mention of this special behaviour, So my question is why? My question is why you are looking up the semantics of Python functions on Wikipedia instead of the Python documentation. I don't see any particular discussion of map() there at all. Am I missing something? -- Robert Kern As I said in an answer to Diez B. Roggish, I had been reminded of the behaviour, thought it odd, and looked for other implementations that might have the behaviour via wikipedia. My intension was most definitely NOT to say that Pythons map should do what Wikipedia says slavishly. Sometimes when I pick at these seeming inconsistencies I learn a lot from the c.l.p replies. Someone elses thread on -0.0 versus +0.0 taught me some more on floating point for example. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Mapping None. Why?
On Jun 12, 9:36 pm, Terry Reedy [EMAIL PROTECTED] wrote: Paddy [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] | | Iam wondering why the peculiar behavior of map when the function in | given as None: The 'peculiar behavior' is the same as zip (except for padding short iterators versus truncating long iterators. Map was added years before zip. After that, map(None,...) was kept for back compatibility. In 3.0, the doc for map is Return an iterator that applies function to every item of iterable, yielding the results. If additional iterable arguments are passed, function must take that many arguments and is applied to the items from all iterables in parallel. With multiple iterables, the iterator stops when the shortest iterable is exhausted. Using a map defined with None raises TypeError: 'NoneType' object is not callable tjr I really should get into the habit of reading the 3.0 docs before asking questions :-) My original question came about after answering this query: http://gmcnaughton.livejournal.com/27955.html?thread=70451#t70451 - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: value is in list?
On Jun 12, 11:46 pm, Steven Clark [EMAIL PROTECTED] wrote: Hello , following scenario list_current = [ welcome, search, done, result] list_ldap = [ welcome, hello] result: list_toadd = [ hello] by words said , i want to check if list item from list_ldap exists in list_current if not i want to add it to list_toadd. Thanks! D. list_toadd = [i for i in list_ldap if i not in list_current] seems to work. I'm sure there's a way to do it with set objects as well. -Steven list_current = [ welcome, search, done, result] list_ldap = [ welcome, hello] to_add = set(list_ldap) - set(list_current) to_add set(['hello']) - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Q re documentation Python style
On Jun 8, 10:17 pm, kj [EMAIL PROTECTED] wrote: I'm a Perlhead trying to learn the Way of Python. I like Python overall, but every once in a while I find myself trying to figure out why Python does some things the way it does. At the moment I'm scratching my head over Python's docstrings. As far as I understand this is the standard way to document Python code. I think that's fine for simple functions, but I have some functions that require a very long docstring to document, and somehow I find it a bit disconcerting to stick a few screenfuls of text between the top line of a function definition and its body. Hi Kynn, Strings on their own are also valid statements so if in Perl you might documentbefore the sub statement or even after the function definition then you could put extra information in a tripple quoted string statement before your function and put the bare essentials in the function itself. This would leave the def nearer the body of the function, but I don't know of anyone else that does this. - Paddy. -- http://mail.python.org/mailman/listinfo/python-list
