Re: [Tutor] Preffered way to search posix filesystem
Miles Stevenson wrote: What is interesting is that the latest 2.4 Python docs say that walk() returns a Tuple, which is untrue. It returns a generator object according to type(). This had me heavily confused as to how to use what was returned from walk() and it took a good hour of troubleshooting to figure it out. The docs are correct but maybe a little subtle. They say, walk( top[, topdown=True [, onerror=None]]) walk() generates the file names in a directory tree, by walking the tree either top down or bottom up. For each directory in the tree rooted at directory top (including top itself), it yields a 3-tuple (dirpath, dirnames, filenames). To someone familiar with Python generators, the words generates and yields are strong clues that walk is a generator and when you iterate over it you get tuples. If you are not familiar with this terminology I can see how it would be confusing. OTOH there are two examples in the same section that show correct usage... Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Advise...
Jacob,
Apart from all the other comments you received, here are my thoughts.
I think you could do one more thing to speed up your calculations and
that is to use a more efficient method. The Reimann sum is not a very
efficient.
One simple method that is rahter popular is Simpson's rule.
The calculations are not much more complicated than what you already
have
You then you just need to make sure that the number of intervals are
even.
Johan
Jacob S. wrote:
Hi all.
Long time no see. (About five days, right?)
Anyway, I know the first thing that some of you are going to say is
using eval(). I don't want a whole
guilt trip on security risks and all that. I do not want to share the
code with anyone else while it's on my
computer, and I sure don't have anyone near me that knows python. I
would be surprised if more than 50
people in Portland, IN knew anything about python. So security is not a
problem. I guess what I'm
looking for is someone who knows the Reimann Sum better than I do and
can tell me whether I can do
something to make it more efficient. It's horribly slow with ten
thousand steps-- I don't know the notation
very well, but it loops the loop O(step*(maximum-minimum)) times, which
is horribly sucky.
In case anyone doesn't know, Reimann's sum is the computer's version
of the definite integral, the area
under a curve in a particular domain.
Basic input and output.
If a curve is a straight line, say y = x, the area under the line on an
interval can be found by geometric means.
However, if you use a parabola, or any other function, say y = 3*x**2,
What is the function? 3*x*x
What is the minimum? 2
What is the maximum? 5
117.000435
Which, considering that it is supposed to be exactly 117, It's darn
good. Unfortunately, it also takes about
10 seconds to do all that.
Any suggestions? Any advice? TIA
Jacob Schmidt
from __future__ import division
import psyco
psyco.full()
fofx = raw_input("What is the function? ")
minimum = raw_input("What is the minimum? ")
maximum = raw_input("What is the maximum? ")
minimum = float(minimum)
maximum = float(maximum)
total = 0
step = 10
x = minimum
while minimum = x = maximum:
area = eval(fofx)*1/step
total = total+area
x = x+1/step
print total
#
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[Tutor] How does import work?
Hi all, I am rather new to python. I am trying to write a program using the scipy package. I have come across a problem that confuses me, and I hope that someone could give me an hint on how to solve this. Here is what I do Start idle from scipy.signal.signaltools import * /Traceback (most recent call last): File pyshell#0, line 1, in -toplevel- from scipy.signal.signaltools import * ImportError: No module named signaltools/ So I try the methodic way and this works, giving me access to the functions I need from scipy import * from scipy.signal import * from scipy.signal.signaltools import * Now what confuses me is that when I put the above three lines in a file (of course without the ) and execute them I get a long error message. / Traceback (most recent call last): File /home/johan/pyton/import_test.py, line 5, in -toplevel- from scipy.signal import * File /usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py, line 270, in __getattr__ module = self._ppimport_importer() File /usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py, line 233, in _ppimport_importer raise PPImportError,\ PPImportError: Traceback (most recent call last): File /usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py, line 243, in _ppimport_importer module = __import__(name,None,None,['*']) File /usr/lib/python2.3/site-packages/scipy/signal/__init__.py, line 11, in ? File /usr/lib/python2.3/site-packages/scipy/signal/ltisys.py, line 14, in ? File /usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py, line 270, in __getattr__ module = self._ppimport_importer() File /usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py, line 233, in _ppimport_importer raise PPImportError,\ PPImportError: Traceback (most recent call last): File /usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py, line 243, in _ppimport_importer module = __import__(name,None,None,['*']) File /usr/lib/python2.3/site-packages/Numeric/Matrix.py, line 5, in ? import LinearAlgebra File /usr/local/lib/python2.3/site-packages/Numeric/LinearAlgebra.py, line 8, in ? import lapack_lite ImportError: /usr/local/lib/python2.3/site-packages/Numeric/lapack_lite.so: undefined symbol: dgesdd_/ What I dont understand is how can the import statements work, when I type them in manually in IDLE and not when I execute them in a file? Has anyone come across this type of behavior before? Johan ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Naming conventions (was: Should this be a list comprehension or something?
On Wed, 26 Jan 2005, Sean Perry wrote: And now, for the pedant in me. I would recommend against naming functions with initial capital letters. In many languages, this implies a new type (like your Water class). so CombineWater should be combineWater. I hate hate hate hate hate camelcase and will never use it. In my book, if the name has *any* capitals in it, the first letter is capitalized, too. Anything else is unaesthetic. To me, when I have names that are composed of multiple words (say, rice quantity), I have two approaches: distinguishing the words by case (RiceQuantity) or separating by underscores (rice_quantity). I never confuse classes/instances and methods, because I use noun phrases for classes and instances (HeatedWater, VerifiedInput) and verb phrases for the methods (CombineWater, CookRice). I suppose I could get confusion, for example, when the combination either a noun phrase or verb phrase (SoundOut: is that a name describing the Sound that's being put Out, or is it a method that's is tentatively Sounding Out somthing?) but so far that hasn't been an issue for me. Of course in my case, I write code only for myself, so I have the luxury of not worrying about what Joe in the next cubicle is doing, and what Jane will do when she's trying to read Bob's and my code together. So I have the luxury of turning my nose up at camelCase. I should add that, the one time I made changes to someone else's Python code for release (a minor patch to nntplib.py), I used the same case conventions already in place in the module. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Control flow
Hi there, I have this logic that I cannot wrap my mind it: def go_jogging(): # go out and jog return if ( bad_weather =='y' ): # ask user only if weather is bad. b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() else: # program should exit now else: go_jogging() I can't get the program to stop processing further in the middle (apparently neither exit nor goto-label exist in Python, sorry for the C++ mindset) so I used exception to achieve what I want. I know in that example you could probably manipulate the logic so that program ends at the bottom of the if-tree. My question is then how to exit in the middle of a if-then-else tree? Thanks, Gilbert. try: if ( bad_weather =='y' ): b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() else: raise Exception( quit ) else: go_jogging() except Exception, inst: print Program exits now ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Control flow
Gilbert Tsang wrote: Hi there, I have this logic that I cannot wrap my mind it: def go_jogging(): # go out and jog return if ( bad_weather =='y' ): # ask user only if weather is bad. b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() else: # program should exit now else: go_jogging() I can't get the program to stop processing further in the middle (apparently neither exit nor goto-label exist in Python, sorry for the C++ mindset) so I used exception to achieve what I want. I know in that example you could probably manipulate the logic so that program ends at the bottom of the if-tree. My question is then how to exit in the middle of a if-then-else tree? Thanks, Gilbert. try: if ( bad_weather =='y' ): b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() else: raise Exception( quit ) else: go_jogging() except Exception, inst: print Program exits now ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor Well, if its in a function you can just do return instead of raise Exception(quit) since the function exits once it returns something. It's sort of the same as the following: Say you have a recursive function fact(n) which takes in a number and returns the factorial of that number. One way to code this would be: def fact(n): if n 3: return n*fact(n-1) else: return 2*n However, since the function 'exits' after a return statement, it saves space in general to do the following: def fact(n): if n 3: return n*fact(n-1) return 2*n Because the only way return 2*n will be reached is if n is smaller than or equal to three, which is what we wanted anyway. BTW, the way this function works is like this: Let's say you want to calculate fact(10). 10 is greater than 3, so the program calculates 10*fact(9) and so on until fact(3) is reached, at which point it will return 10*(9*(8*(7*(6*(5*(4*(6))) (6 is 2 * 3). or the factorial of 10. I probably didn't do too good a job explaining that, and that's probably not the most efficient implementation (it breaks @ around fact(1000) by default, and around fact(11462) when you use sys.setrecursionlimit(2000) (11462 is as high as it'll go on my machine)), so please feel free to ask questions. HTH, Orri -- Email: singingxduck AT gmail DOT com AIM: singingxduck Programming Python for the fun of it. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Control flow
Gilbert Tsang wrote: Hi there, I have this logic that I cannot wrap my mind it: def go_jogging(): # go out and jog return if ( bad_weather =='y' ): # ask user only if weather is bad. b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() else: # program should exit now else: go_jogging() I can't get the program to stop processing further in the middle (apparently neither exit nor goto-label exist in Python, sorry for the C++ mindset) so I used exception to achieve what I want. I know in that example you could probably manipulate the logic so that program ends at the bottom of the if-tree. My question is then how to exit in the middle of a if-then-else tree? Thanks, Gilbert. try: if ( bad_weather =='y' ): b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() else: raise Exception( quit ) else: go_jogging() except Exception, inst: print Program exits now ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor Well, if its in a function you can just do return instead of raise Exception(quit) since the function exits once it returns something. It's sort of the same as the following: Say you have a recursive function fact(n) which takes in a number and returns the factorial of that number. One way to code this would be: def fact(n): if n 3: return n*fact(n-1) else: return 2*n However, since the function 'exits' after a return statement, it saves space in general to do the following: def fact(n): if n 3: return n*fact(n-1) return 2*n Because the only way return 2*n will be reached is if n is smaller than or equal to three, which is what we wanted anyway. BTW, the way this function works is like this: Let's say you want to calculate fact(10). 10 is greater than 3, so the program calculates 10*fact(9) and so on until fact(3) is reached, at which point it will return 10*(9*(8*(7*(6*(5*(4*(6))) (6 is 2 * 3). or the factorial of 10. I probably didn't do too good a job explaining that, and that's probably not the most efficient implementation (it breaks @ around fact(1000) by default, and around fact(11462) when you use sys.setrecursionlimit(2000) (11462 is as high as it'll go on my machine)), so please feel free to ask questions. HTH, Orri -- Email: singingxduck AT gmail DOT com AIM: singingxduck Programming Python for the fun of it. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Should this be a list comprehension or something?
I don't get this joke, but it sounds like the basis for it would be interesting. Can you explain? After sending my last message I was browsing the Eiffel site and found an example of the IDE. Its here: http://archive.eiffel.com/eiffel/nutshell.html and you scroll down to the question: What does a class look like? The code under that is a direct cut n paste from their commercial editor. (The freeware version is in a screenshot a little bit above...) Note the use of a proportional font(Arial?) as well as the documentation like style of Eiffel in general... Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Should this be a list comprehension or something?
On Fri, 28 Jan 2005, Alan Gauld wrote: Its not so much a criterion that they *should* be used that way, its just that its what they do. A list comprehension creates a list! Thats why they are called *list* comprehensions. :-) See, I'd always figured that the reason it was called a list comprehension was because the list comprehension operated on a list, and the operation was comprehension. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Control flow
SEveral solutions here. The best is to restructure the code a little: def go_jogging(): # go out and jog return if not bad_weather == 'y': # where is this initially set BTW? go_jogging() else # ask user only if weather is bad. b = input ( Weather is really bad, still go out to jog?[y/n] ) if b == 'y': go_jogging() Its shorter, simpler and makes the most common case the default (assuming that bad weather is the exception!) I can't get the program to stop processing further in the middle Good, that would be really bad practice from a structured programming point of view. :-) But if you really, really must, you could always call raise SystemExit which bombs out more or less immediately - like exit() in C C++ mindset) so I used exception to achieve what I want. Yes thats ok, and the exception to use is already there... example you could probably manipulate the logic so that program ends at the bottom of the if-tree. My question is then how to exit in the middle of a if-then-else tree? You should never need to. One of the things that structured programming (Edsgar Dijkstra to be precise) showed was that you can *always* rearrange things so that goto's and intermediate exits are not needed and indeed can introduce an extra level of complexity and error. Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Naming conventions
Terry Carroll wrote: On Fri, 28 Jan 2005, Kent Johnson wrote: Separating with underscores is quite common in the Python community, actually it is the preferred spelling for library modules. So maybe you should adopt that, just to reduce the confusion when your code does have an encounter with the outside world :-) I'm a lawyer by trade; my work is *supposed* to confuse the outside world! Then you are using the wrong language entirely. May I suggest Brainf*ck or INTERCAL or Whitespace? http://www.thefreecountry.com/compilers/esoteric.shtml Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
RE: [Tutor] Diffing two files.
Kent What I need to do is find what should be common and see if it really is. I have two output files...The output files will have a bunch of systems stuff then the text of interest and then a bunch more systems stuff. The systems stuff may be different for each file but the text of interest will always have a fixed line in front of it and behind it. The idea is to get the text of interest (using the known beginning and ending flags in the text) from each file and then check to make sure the text of interest is the same in both files. I have not done much text stuff so this is new territory for me. I will take a look at difflib. Thanks again John Ertl Simplified example of a text files. Sldfsdf Sdfsdfsf Sdfsdfsdfwefs Sdcfasdsgerg Vsadgfasgdbgdfgsdf -Beginning flag This Text Should be The Same in the other file. -Ending flag Sdfsdfsdfsd Sdfsdfsdfasd Sdfsadfsdf Sdfsadfasdf Sdfsdfasd Sdfasdf s -Original Message- From: Kent Johnson [mailto:[EMAIL PROTECTED] Sent: Friday, January 28, 2005 15:23 Cc: Tutor@python.org Subject: Re: [Tutor] Diffing two files. You don't really say what you are trying to accomplish. Do you want to identify the common text, or find the pieces that differ? If the common text is always the same and you know it ahead of time, you can just search the lines of each file to find it. If you need to identify the common part, difflib might be useful. There is an example on this page of finding matching blocks of two sequences: http://docs.python.org/lib/sequencematcher-examples.html In your case the sequences will be lists of lines rather than strings (which are sequences of characters) Kent Ertl, John wrote: All, I have two text files that should contain a section of text that is the same. Luckily the section of text has a defined beginning and end. It looks like the most straightforward thing would be to read the targeted text from each file (only 50 lines or so) into lists and then compare the lists. I would think I could use sets to find a unique list (hopefully there would not be anything)...or I could do line by line comparison. Any advise on what is the better method. Should I avoid the list comparison approach...is there a built in way of comparing entire files instead of dealing explicitly with the lines? Thanks, John Ertl ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
