Re: Extending dict (dict's) to allow for multidimensional dictionary
On 2011-03-05 12:05:43 -0800, Paul Rubin said: Ravi ra.ravi@gmail.com writes: I can extend dictionary to allow for the my own special look-up tables. However now I want to be able to define multidimensional dictionary which supports look-up like this: d[1]['abc'][40] = 'dummy' Why do that anyway? You can use a tuple as a subscript: d[1,'abc',40] = 'dummy' Depends on the use cases. If you only want to access d by a full tuple, that's fine. If you want to access all the entries below d[1], it's a problem. And if you want to access entities randomly by an arbitrary dimension, you probably want a database (as others have pointed out). -Tom -- http://mail.python.org/mailman/listinfo/python-list
examples of realistic multiprocessing usage?
I'm trying to multiprocess my python code to take advantage of multiple cores. I've read the module docs for threading and multiprocessing, and I've done some web searches. All the examples I've found are too simple: the processes take simple inputs and compute a simple value. My problem involves lots of processes, complex data structures, and potentially lots of results. It doesn't map cleanly into a Queue, Pool, Manager or Listener/Client example from the python docs. Instead of explaining my problem and asking for design suggestions, I'll ask: is there a compendium of realistic Python multiprocessing examples somewhere? Or an open source project to look at? Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Not clear about the dot notation
On 2011-01-16 11:59:11 -0800, Zeynel said: What does vote.vote refer to in this snippet? def txn(): quote = Quote.get_by_id(quote_id) vote = Vote.get_by_key_name(key_names = user.email(), parent = quote) if vote is None: vote = Vote(key_name = user.email(), parent = quote) if vote.vote == newvote: return quote.votesum = quote.votesum - vote.vote + newvote vote.vote = newvote from here: http://code.google.com/appengine/articles/overheard.html vote refers to the Vote instance. vote.vote refers to the instance variable in that instance: vote: The value of 1 for like, -1 for dislike. Confusing choice of names, in my opinion. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Not clear about the dot notation
On 2011-01-16 12:44:35 -0800, Zeynel said: On Jan 16, 3:24 pm, TomF tomf.sess...@gmail.com wrote: vote refers to the Vote instance. So he must have instatiated previously like vote = Vote() is this correct? Yes. So I have a model class Item(db.Model): title = db.StringProperty() url = db.StringProperty() date = db.DateTimeProperty(auto_now_add=True) author = db.UserProperty() and to write to the database I do item = Item() item.title = self.request.get(title) item.url = self.request.get(url) item.author = users.get_current_user() item.put() self.redirect(/newest) so his vote.vote is like my item.url ? I believe so. Though you're now talking about an extension to db.Model which looks like it's doing a lot more behind the scenes than a simple variable access. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: examples of realistic multiprocessing usage?
On 2011-01-16 19:16:15 -0800, Dan Stromberg said: On Sun, Jan 16, 2011 at 11:05 AM, TomF tomf.sess...@gmail.com wrote: I'm trying to multiprocess my python code to take advantage of multiple cores. I've read the module docs for threading and multiprocessing, and I've done some web searches. All the examples I've found are too simple: the processes take simple inputs and compute a simple value. My problem involves lots of processes, complex data structures, and potentially lots of results. It doesn't map cleanly into a Queue, Pool, Manager or Listener/Client example from the python docs. Instead of explaining my problem and asking for design suggestions, I'll ask: is there a compendium of realistic Python multiprocessing examples somewhere? Or an open source project to look at? I'm unaware of a big archive of projects that use multiprocessing, but maybe one of the free code search engines could help with that. It sounds like you're planning to use mutable shared state, which is generally best avoided if at all possible, in concurrent programming - because mutable shared state tends to slow down things quite a bit. I'm trying to avoid mutable shared state since I've read the cautions against it. I think it's possible for each worker to compute changes and return them back to the parent (and have the parent coordinate all changes) without too much overhead. So far It looks like multiprocessing.Pool.apply_async is the best match to what I want. One difficulty is that there is a queue of work to be done and a queue of results to be incorporated back into the parent; there is no one-to-one correspondence between the two. It's not obvious to me how to coordinate the queues in a natural way to avoid deadlock or starvation. But if you must have mutable shared state that's more complex than a basic scalar or homogeneous array, I believe the multiprocessing module would have you use a server process manager. I've looked into Manager but I don't really understand the trade-offs. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: examples of realistic multiprocessing usage?
On 2011-01-16 20:57:41 -0800, Adam Skutt said: On Jan 16, 11:39 pm, TomF tomf.sess...@gmail.com wrote: One difficulty is that there is a queue of work to be done and a queue of results to be incorporated back into the parent; there is no one-to-one correspondence between the two. It's not obvious to me how to coordinate the queues in a natural way to avoid deadlock or starvation. Depends on what you are doing. If you can enqueue all the jobs before waiting for your results, then two queues are adequate. The first queue is jobs to be accomplished, the second queue is the results. The items you put on the result queue have both the result and some sort of id so the results can be ordered after the fact. Your parent thread of execution (thread hereafter) then: 1. Adds jobs to the queue 2. Blocks until all the results are returned. Given that you suggested that there isn't a 1:1 correspondence between jobs and results, have the queue support a message saying, 'Job X is done'. You're finished when all jobs send such a message. 3. Sorts the results into the desired ordered. 4. Acts on them. If you cannot enqueue all the jobs before waiting for the results, I suggest turning the problem into a pipeline, such that the thread submitting the jobs and the thread acting on the results are different: submitter - job processor - results processor. Adam Thanks for your reply. I can enqueue all the jobs before waiting for the results, it's just that I want the parent to process the results as they come back. I don't want the parent to block until all results are returned. I was hoping the Pool module had a test for whether all processes were done, but I guess it isn't hard to keep track of that myself. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: True lists in python?
On 2010-12-18 22:18:07 -0800, Dmitry Groshev said: Is there any way to use a true lists (with O(c) insertion/deletion and O(n) search) in python? For example, to make things like reversing part of the list with a constant time. I assume you mean a C extension that implements doubly linked lists (reversing part of a list is only constant time if the list is doubly-linked). I'm not aware of one. A longer answer is that many high level languages (Python, Perl, Ruby) don't bother implementing simple linked lists because they're not very useful. Instead they use hybrid data structures that can operate as lists and arrays with flexibility and acceptable costs. And if you need greater speed you usually go to special purpose arrays (for constant time access) rather than lists. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Comparisons of incompatible types
On 2010-12-07 16:09:17 -0800, Mark Wooding said:
Carl Banks pavlovevide...@gmail.com writes:
I think that feeling the need to sort non-homogenous lists is
indictative of bad design.
Here's a reason you might want to.
You're given an object, and you want to compute a hash of it. (Maybe
you want to see whether someone else's object is the same as yours, but
don't want to disclose the actual object, say.) To hash it, you'll need
to serialize it somehow. But here's a problem: objects like
dictionaries and sets don't impose an ordering on their elements. For
example, the set { 1, 'two' } is the same as the set { 'two', 1 } -- but
iterating the two might well yield the elements in a different order.
(The internal details of a hash table tend to reflect the history of
operations on the hash table as well as its current contents.)
The obvious answer is to apply a canonical ordering to unordered objects
like sets and dictionaries. A set can be serialized with its elements
in ascending order; a dictionary can be serialized as key/value pairs
with the keys in ascending order. But to do this, you need an
(arbitrary, total) order on all objects which might be set elements or
dictionary keys. The order also needs to be dependent only on the
objects' serializable values, and not on any incidental facts such as
memory addresses or whatever.
I have no argument that there might be an extra-logical use for such an
ordering which you might find convenient. This is the point you're
making. sort() and sorted() both take a cmp argument for this sort of
thing. My complaint is with Python adopting nonsensical semantics
(shoe 7) to accomodate it.
By analogy, I often find it convenient to have division by zero return
0 to the caller for use in calculations. But if Python defined 0/0==0
I'd consider it broken.
-Tom
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Comparisons of incompatible types
I'm aggravated by this behavior in python: x = 4 print x 7# prints False The issue, of course, is comparisons of incompatible types. In most languages this throws an error (in Perl the types are converted silently). In Python this comparison fails silently. The documentation says: objects of different types *always* compare unequal, and are ordered consistently but arbitrarily. I can't imagine why this design decision was made. I've been bitten by this several times (reading data from a file and not converting the numbers before comparison). Can I get this to throw an error instead of failing silently? Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Comparisons of incompatible types
On 2010-12-06 09:04:00 -0800, Peter Otten said: TomF wrote: I'm aggravated by this behavior in python: x = 4 print x 7# prints False The issue, of course, is comparisons of incompatible types. In most languages this throws an error (in Perl the types are converted silently). In Python this comparison fails silently. The documentation says: objects of different types *always* compare unequal, and are ordered consistently but arbitrarily. I can't imagine why this design decision was made. I've been bitten by this several times (reading data from a file and not converting the numbers before comparison). Can I get this to throw an error instead of failing silently? This change would break a lot of code, so it could not be made within the 2.x series. However: Python 3.1.1+ (r311:74480, Nov 2 2009, 15:45:00) [GCC 4.4.1] on linux2 Type help, copyright, credits or license for more information. 4 7 Traceback (most recent call last): File stdin, line 1, in module TypeError: unorderable types: str() int() Thanks. I was hoping there was something I could do for 2.x but I suppose this will have to do. But I'm mystified by your statement, this change would break a lot of code. Given that the semantics are virtually random, how could code depend on this? -Tom -- http://mail.python.org/mailman/listinfo/python-list
Request for comments on a design
I have a program that manipulates lots of very large indices, which I implement as bit vectors (via the bitarray module). These are too large to keep all of them in memory so I have to come up with a way to cache and load them from disk as necessary. I've been reading about weak references and it looks like they may be what I want. My idea is to use a WeakValueDictionary to hold references to these bitarrays, so Python can decide when to garbage collect them. I then keep a key-value database of them (via bsddb) on disk and load them when necessary. The basic idea for accessing one of these indexes is: _idx_to_bitvector_dict = weakref.WeakValueDictionary() def retrieve_index(idx): if idx in _idx_to_bitvector_dict and _idx_to_bitvector_dict[idx] is not None: return _idx_to_bitvector_dict[idx] else: # it's been gc'd bv_str = bitvector_from_db[idx]# Load from bsddb bv = cPickle.loads(bv_str)# Deserialize the string _idx_to_bitvector_dict[idx] = bv # Re-initialize the weak dict element return bv Hopefully that's not too confusing. Comments on this approach? I'm wondering whether the weakref stuff isn't duplicating some of the caching that bsddb might be doing. Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Request for comments on a design
On 2010-10-23 01:50:53 -0700, Peter Otten said: TomF wrote: I have a program that manipulates lots of very large indices, which I implement as bit vectors (via the bitarray module). These are too large to keep all of them in memory so I have to come up with a way to cache and load them from disk as necessary. I've been reading about weak references and it looks like they may be what I want. My idea is to use a WeakValueDictionary to hold references to these bitarrays, so Python can decide when to garbage collect them. I then keep a key-value database of them (via bsddb) on disk and load them when necessary. The basic idea for accessing one of these indexes is: _idx_to_bitvector_dict = weakref.WeakValueDictionary() In a well written script that cache will be almost empty. You should compare the weakref approach against a least-recently-used caching strategy. In newer Pythons you can use collections.OrderedDict to implement an LRU cache or use the functools.lru_cache decorator. I don't know what your first sentence means, but thanks for pointers to the LRU stuff. Maintaining my own LRU cache might be a better way to go. At least I'll have more control. Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Deferring a function call
Thanks for the ideas, everyone. functools.partial and lambda expressions seem like a more pythonic way of doing what I want. I don't know whether they're actually more efficient or better, but at least they eliminate the need to carry args around separately. I'd forgotten Python has a sched module in its standard library. It may be overkill for what I want to do but I'll take a look. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Deferring a function call
I'm writing a simple simulator, and I want to schedule an action to occur at a later time. Basically, at some later point I want to call a function f(a, b, c). But the values of a, b and c are determined at the current time. One way way to do this is to keep a list of entries of the form [[TIME, FN, ARGS]...] and at simulated time TIME do: apply(FN, ARGS) Aside from the fact that apply is deprecated, it seems like there should be a cleaner (possibly more Pythonic) way to do this. Ideas? -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: please help explain this result
On 2010-10-17 10:21:36 -0700, Paul Kölle said:
Am 17.10.2010 13:48, schrieb Steven D'Aprano:
On Sun, 17 Oct 2010 03:58:21 -0700, Yingjie Lan wrote:
Hi,
I played with an example related to namespaces/scoping. The result is a
little confusing:
[snip example of UnboundLocalError]
Python's scoping rules are such that if you assign to a variable inside a
function, it is treated as a local. In your function, you do this:
def f():
a = a + 1
Since a is treated as a local, when you enter the function the local a is
unbound -- it does not have a value. So the right hand side fails, since
local a does not exist, and you get an UnboundLocalError. You are trying
to get the value of local a when it doesn't have a value.
Steven's explanation is correct. In your example below you're altering
portions of a global data structure, not reassigning a global variable.
Put another way, there is a significant difference between:
a = 7
and:
a['x'] = 7
Only the first reassigns a global variable.
-Tom
Oh really? Can you explain the following?
a = {}
def foo():
... a['a'] = 'lowercase a'
... print a.keys()
...
foo()
['a']
a
{'a': 'lowercase a'}
def bar():
... a['b'] = a['a'].replace('a', 'b')
...
bar()
a
{'a': 'lowercase a', 'b': 'lowercbse b'}
cheers
Paul
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Re: Global variables for python applications
On 2010-05-19 07:34:37 -0700, Steven D'Aprano said: # Untested. def verbose_print(arg, level, verbosity=1): if level = verbosity: print arg def my_function(arg): my_print(arg, level=2) return arg.upper() if __name__ == '__main__': if '--verbose' in sys.argv: my_print = functools.partial(verbose_print, verbosity=2) elif '--quiet' in sys.argv: my_print = functools.partial(verbose_print, verbosity=0) my_function(hello world) Note that although there is no verbosity global setting, every function that calls my_print will do the right thing (unless I've got the test backwards...), and if a function needs to override the implicit verbosity setting, it can just call verbose_print directly. -- http://mail.python.org/mailman/listinfo/python-list
Re: Global variables for python applications
On 2010-05-16 12:27:21 -0700, christian schulze said: On 16 Mai, 20:20, James Mills prolo...@shortcircuit.net.au wrote: On Mon, May 17, 2010 at 4:00 AM, Krister Svanlund krister.svanl...@gmail.com wrote: On Sun, May 16, 2010 at 7:50 PM, AON LAZIO aonla...@gmail.com wrote: How can I set up global variables for the entire python applications? Like I can call and set this variables in any .py files. Think of it as a global variable in a single .py file but thisis for the entire application. First: Do NOT use global variables, it is bad practice and will eventually give you loads of s**t. But if you want to create global variables in python I do believe it is possible to specify them in a .py file and then simply import it as a module in your application. If you change one value in a module the change will be available in all places you imported that module in. The only place global variables are considered somewhat acceptable are as constants in a module shared as a static value. Anything else should be an object that you share. Don't get into the habit of using global variables! --james Exactly! Python's OOP is awesome. Use it. Global vars used as anything but constants is bad practice. It isn't that much work to implement that. Let's say you have a bunch of globals, one of which is a verbose flag. If I understand the difference, using a module gbls.py: # in gbls.py verbose = False # elsewhere: import gbls gbls.verbose = True Using a class: # In the main module: class gbls(object): def __init__(self, verbose=False): self.verbose = verbose my_globals = gbls.gbls(verbose=True) ... some_function(my_globals, ...) If this is what you have in mind, I'm not really seeing how one is good practice and the other is bad. The OOP method is more verbose (no pun intended) and I don't see how I'm any less likely to shoot myself in the foot with it. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Django as exemplary design
On 2010-05-06 18:20:02 -0700, Trent Nelson said: I'm interested in improving my python design by studying a large, well-designed codebase. I'll tell you one of the best ways to improve your Python code: attend one of Raymond Hettinger's Code Clinic workshops at a Python conference and put some up of your work up on the projector for 20+ developers to rip apart, line by line ;-) You'll pick up more in 30 minutes than you ever thought possible. I don't doubt it. But I'm not really interested in line (micro) level code issues at the moment. Not that my code couldn't stand being improved, but I'm more interested in seeing how medium/large OO python systems are designed. If I could get this from a book I would, but I suspect I need to study real code. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Django as exemplary design
Thanks to everyone for their comments. On 2010-05-04 07:11:08 -0700, alex23 said: TomF tomf.sess...@gmail.com wrote: I'm interested in improving my python design by studying a large, well-designed codebase. Someone (not a python programmer) suggested Django. I realize that Django is popular, but can someone comment on whether its code is well-designed and worth studying? Here's a viewpoint that says no: http://mockit.blogspot.com/2010/04/mess-djangos-in.html There's a lot of good counterpoint in the comments too. I read most of the discussion. Yep, there is a LOT of disagreement about the code quality. I guess I'll dig in and see whether I can learn anything. (I also think there's value to be gained in studying _bad_ code, too...) True, although whether that's time well spent is another question. Regards, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Django as exemplary design
I'm interested in improving my python design by studying a large, well-designed codebase. Someone (not a python programmer) suggested Django. I realize that Django is popular, but can someone comment on whether its code is well-designed and worth studying? Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: getting a string as the return value from a system command
On 2010-04-16 12:06:13 -0700, Catherine Moroney said: Hello, I want to call a system command (such as uname) that returns a string, and then store that output in a string variable in my python program. What is the recommended/most-concise way of doing this? I could always create a temporary file, call the subprocess.Popen module with the temporary file as the stdout argument, and then re-open that temporary file and read in its contents. This seems to be awfully long way of doing this, and I was wondering about alternate ways of accomplishing this task. In pseudocode, I would like to be able to do something like: hostinfo = subprocess.Popen(uname -srvi) and have hostinfo be a string containing the result of issuing the uname command. Here is the way I do it: import os hostinfo = os.popen(uname -srvi).readline().strip() (I add a strip() call to get rid of the trailing newline.) os.popen has been replaced by the subprocess module, so I suppose the new preferred method is: from subprocess import Popen, PIPE hostinfo = Popen([uname, -srvi], stdout=PIPE).communicate()[0].strip() Looks ugly to me, but there we are. -Tom -- http://mail.python.org/mailman/listinfo/python-list
distutils examples?
I'm packaging up a program with distutils and I've run into problems trying to get setup.py right. It's not a standalone package; it's a script plus modules, data files and documentation. I've been over the distutils documentation but I'm having trouble getting the package_data and data_files correct. Is there a repository of distutils examples somewhere that I can look at? The documentation is not particularly instructive for me. Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: (a==b) ? 'Yes' : 'No'
On 2010-03-31 00:57:51 -0700, Peter Otten __pete...@web.de said: Pierre Quentel wrote: I'm surprised nobody proposed a solution with itertools ;-) next(itertools.takewhile(lambda _: a == b, [yes]), no) You spoke to soon :) I salute you, sir, for upholding the standards of this group. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: sum for sequences?
On 2010-03-24 14:07:24 -0700, Steven D'Aprano ste...@remove.this.cybersource.com.au said: On Wed, 24 Mar 2010 15:29:07 +, kj wrote: Is there a sequence-oriented equivalent to the sum built-in? E.g.: seq_sum(((1, 2), (5, 6))) -- (1, 2) + (5, 6) -- (1, 2, 5, 6) ? Yes, sum. help(sum) is your friend. You might not want to be so glib. The sum doc sure doesn't sound like it should work on lists. Returns the sum of a sequence of numbers (NOT strings) plus the value of parameter 'start' (which defaults to 0). -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: to pass self or not to pass self
On 2010-03-15 09:39:50 -0700, lallous elias.bachaal...@gmail.com said:
Hello,
Learning Python from the help file and online resources can leave one
with many gaps. Can someone comment on the following:
# -
class X:
T = 1
def f1(self, arg):
print f1, arg=%d % arg
def f2(self, arg):
print f2, arg=%d % arg
def f3(self, arg):
print f3, arg=%d % arg
# this:
F = f2
# versus this:
func_tbl = { 1: f1, 2: f2, 3: f3 }
def test1(self, n, arg):
# why passing 'self' is needed?
return self.func_tbl[n](self, arg)
def test2(self):
f = self.f1
f(6)
f = self.F
# why passing self is not needed?
f(87)
# -
x = X()
x.test1(1, 5)
print '--'
x.test2()
Why in test1() when it uses the class variable func_tbl we still need
to pass self, but in test2() we don't ?
What is the difference between the reference in 'F' and 'func_tbl' ?
I recommend putting print statements into your code like this:
def test1(self, n, arg):
print In test1, I'm calling a %s % self.func_tbl[n]
return self.func_tbl[n](self, arg)
def test2(self):
f = self.f1
print Now in test2, I'm calling a %s % f
f(6)
Bottom line: You're calling different things. Your func_tbl is a dict
of functions, not methods.
-Tom
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Re: cpan for python?
On 2010-03-02 19:59:01 -0800, Lie Ryan lie.1...@gmail.com said: On 03/03/2010 09:47 AM, TomF wrote: On 2010-03-02 13:14:50 -0800, R Fritz rfr...@u.washington.edu said: On 2010-02-28 06:31:56 -0800, sstein...@gmail.com said: On Feb 28, 2010, at 9:28 AM, Someone Something wrote: Is there something like cpan for python? I like python's syntax, but Iuse perl because of cpan and the tremendous modules that it has. -- Please search the mailing list archives. This subject has been discussed to absolute death. But somehow the question is not in the FAQ, though the answer is. See: http://www.python.org/doc/faq/library/#how-do-i-find-a-module-or-application-to-perform-task-x There is also a program called cpan, distributed with Perl. It is used for searching, downloading, installing and testing modules from the CPAN repository. It's far more extensive than setuptools. AFAIK the python community has developed nothing like it. python have easy_install easy_install is part of setuptools. As I said, nothing like cpan. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: cpan for python?
On 2010-03-02 13:14:50 -0800, R Fritz rfr...@u.washington.edu said: On 2010-02-28 06:31:56 -0800, sstein...@gmail.com said: On Feb 28, 2010, at 9:28 AM, Someone Something wrote: Is there something like cpan for python? I like python's syntax, but Iuse perl because of cpan and the tremendous modules that it has. -- Please search the mailing list archives. This subject has been discussed to absolute death. But somehow the question is not in the FAQ, though the answer is. See: http://www.python.org/doc/faq/library/#how-do-i-find-a-module-or-application-to-perform-task-x There is also a program called cpan, distributed with Perl. It is used for searching, downloading, installing and testing modules from the CPAN repository. It's far more extensive than setuptools. AFAIK the python community has developed nothing like it. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: formatting a number as percentage
On 2010-02-21 09:53:45 -0800, vsoler vicente.so...@gmail.com said:
I'm trying to print .7 as 70%
I've tried:
print format(.7,'%%')
.7.format('%%')
but neither works. I don't know what the syntax is...
print Grade is {0:%}.format(.87)
Grade is 87.00%
or if you want to suppress those trailing zeroes:
print Grade is {0:.0%}.format(.87)
Grade is 87%
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Re: Is there a simple way to find the list index to the max value?
On 2010-02-16 11:44:45 -0800, a...@pythoncraft.com (Aahz) said: In article 4b7a91b1.6030...@lonetwin.net, steve st...@lonetwin.net wrote: On 02/16/2010 05:49 PM, W. eWatson wrote: See Subject. a = [1,4,9,3]. Find max, 9, then index to it, 2. The most obvious would be a.index(max(a)). Is that what you wanted ? The disadvantage of that is that it's O(2N) instead of O(N). I don't think you understand order notation. There's no such thing as O(2N). To answer the original question, how about: max(enumerate(l), key=lambda x: x[1])[0] As to whether this is faster than index(max()), you'd have to time it. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Python system with exemplary organization/coding style
On 2009-05-14 16:18:07 -0700, CTO debat...@gmail.com said: On May 14, 7:01 pm, TomF tomf.sess...@gmail.com wrote: I'm looking for a medium-sized Python system with very good coding style and good code organization, so I can learn from it. I'm reading various books on Python with advice on such things but I'd prefer to see a real system. By medium-sized I mean 5-20 classes, 5-20 files, etc; a code base that has some complexity but isn't overwhelming. Thanks, -Tom I'd recommend screenlets. Good documentation and pretty good style, and they have some external dependencies so you can see how that operates, and of course you can see what your code is and isn't doing pretty quickly. URL: http://www.screenlets.org Thanks, this does look pretty good. Too bad it's grapics oriented, but I suppose I can filter out the graphics dependencies. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Python system with exemplary organization/coding style
I'm looking for a medium-sized Python system with very good coding style and good code organization, so I can learn from it. I'm reading various books on Python with advice on such things but I'd prefer to see a real system. By medium-sized I mean 5-20 classes, 5-20 files, etc; a code base that has some complexity but isn't overwhelming. Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Simple way of handling errors
On 2009-05-07 01:01:57 -0700, Peter Otten __pete...@web.de said: TomF wrote: As a relative newcomer to Python, I like it a lot but I'm dismayed at the difficulty of handling simple errors. In Perl if you want to anticipate a file-not-found error you can simply do: open($file) or die(open($file): $!); and you get an intelligible error message. In Python, to get the same thing it appears you need at least: try: f=open(file) except IOError, err: print open(%s): got %s % (file, err.strerror) exit(-1) Is there a simpler interface or idiom for handling such errors? I appreciate that Python's exception handling is much more sophisticated but often I don't need it. -Tom While you are making the transition you could write from perl_idioms import open_or_die f = open_or_die(does-not-exist) with the perl_idioms module looking like import sys def open_or_die(*args): try: return open(*args) except IOError, e: sys.exit(e) Peter Thanks. Rolling my own error module for common errors may be the best way to go. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Simple way of handling errors
As a relative newcomer to Python, I like it a lot but I'm dismayed at the difficulty of handling simple errors. In Perl if you want to anticipate a file-not-found error you can simply do: open($file) or die(open($file): $!); and you get an intelligible error message. In Python, to get the same thing it appears you need at least: try: f=open(file) except IOError, err: print open(%s): got %s % (file, err.strerror) exit(-1) Is there a simpler interface or idiom for handling such errors? I appreciate that Python's exception handling is much more sophisticated but often I don't need it. -Tom -- http://mail.python.org/mailman/listinfo/python-list
Re: Simple way of handling errors
On 2009-05-06 19:41:29 -0700, Steven D'Aprano ste...@remove.this.cybersource.com.au said: On Wed, 06 May 2009 16:40:19 -0700, TomF wrote: As a relative newcomer to Python, I like it a lot but I'm dismayed at the difficulty of handling simple errors. In Perl if you want to anticipate a file-not-found error you can simply do: open($file) or die(open($file): $!); and you get an intelligible error message. In Python, to get the same thing it appears you need at least: try: f=open(file) except IOError, err: print open(%s): got %s % (file, err.strerror) exit(-1) Functions never fail silently in Python. (At least built-in functions never fail silently. Functions you write yourself can do anything you want.) Well, yes, I'm aware that if you don't handle errors Python barfs out a backtrace. If it fails, you get both a straight-forward error message and a useful traceback: Traceback (most recent call last): File stdin, line 1, in module IOError: [Errno 2] No such file or directory: 'foomanchu' The only reason you would bother going to the time and effort of catching the error, printing your own error message, and then exiting, is if you explicitly want to hide the traceback from the user. Well, to me, exposing the user to such raw backtraces is unprofessional, which is why I try to catch user-caused errors. But I suppose I have an answer to my question. Thanks, -Tom -- http://mail.python.org/mailman/listinfo/python-list
