🌐 Mailman 3 August 2007 - Python-list - python.org

Checking object types
by Robert Dailey Aug. 1, 2007

Aug. 1, 2007

Hi, I'm currently interested in creating an __add__() operator for one of my classes. This class handles both integers and objects its own type, however I don't know how I can perform special add operations depending on which is passed in. Since I haven't seen any evidence of function overloading, I'm assuming I'll have to check the types of the variables passed in inside of my __add__() method. Take the two following examples: vector3(3,4,2) + 5 = vector3(8,9,7) vector3(3,2,1) + vector3(4,5,6) = vector3(7,7,7) Any tips? Thanks.

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Strange problems with subprocess
by Michele Petrazzo Aug. 1, 2007

Aug. 1, 2007

Hi all. I have a simple "ping tester" program that, every 1 minute (execute by linux crontab), create, with subprocess, a "ping -c 1 my_addrs". All work, but sometime (about 1/2 times at a day), I receive this error message: File "/exports/srv-wipex/net_test/ping_tester.py", line 88, in pyPing cmd_p = Popen(cmd, stdout=PIPE, stderr=PIPE) File "subprocess.py", line 543, in __init__ errread, errwrite) File "subprocess.py", line 970, in _execute_child data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB What can be that raise this? Python 2.4 in deb etch Thanks, Michele

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Re: Assertion in list comprehension
by Stargaming Aug. 1, 2007

Aug. 1, 2007

On Wed, 01 Aug 2007 11:28:48 -0500, Chris Mellon wrote: > On 8/1/07, beginner <zyzhu2000(a)gmail.com> wrote: >> Hi, >> >> Does anyone know how to put an assertion in list comprehension? I have >> the following list comprehension, but I want to use an assertion to >> check the contents of rec_stdl. I ended up using another loop which >> essentially duplicates the functions of list comprehension. It just >> look like a waste of coding and computer time to me. >> >> I just wish I could put the assertions into list comprehensions. >> >> x=[(rec_stdl[0].st/10000.0, >> rec_stdl[0].cl, >> rec_stdl[0].bb, >> rec_stdl[0].bo, >> rec_stdl[1].bb, >> rec_stdl[1].bo, >> rec_stdl[0].ex >> ) >> for rec_stdl in rec_by_ex if len(rec_stdl)==2 >> ] >> >> #duplicated loop >> if __debug__: >> for rec_stdl in rec_by_ex: >> l=len(rec_stdl) >> assert(l<=2 and l>0) >> if l==2: >> assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P") >> assert(rec_stdl[0].ex==rec_stdl[1].ex) >> assert(rec_stdl[0].st==rec_stdl[1].st) >> assert(rec_stdl[0].cp==rec_stdl[1].cp) > > First: All your asserts are wrong. Assert is a statement, not a > function. These specific ones will behave as expected, but it's easy to > accidentally write ones that always pass this way. Could you come up with an example? I can only think of accidentally injecting a comma, what would create a (true, in a boolean context) tuple. And, well, if you're only using () for readabilty, this might sometimes look messy when calling assert with the extended syntax:: assert(False), "error text" Where one could expect the construction of a tuple. > Secondly: This is a waste of code, because if __debug__ is not defined > asserts will be skipped by the compiler. You could use the same loop > block for both branches. Well, the `assert` isn't there for no reason, but if you're serious about it, `raise` could be better. > Thirdly: This sort of testing is precisely what unit tests and/or > doctests are for. Huh? What beginner is doing there seems more like input validation than testing. Unit or doctests are meant for testing (and in case of doctests, showing) whether a function works as expected.

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Re: Assertion in list comprehension
by beginner Aug. 1, 2007

Aug. 1, 2007

On Aug 1, 11:28 am, "Chris Mellon" <arka...(a)gmail.com> wrote: > On 8/1/07, beginner <zyzhu2...(a)gmail.com> wrote: > > > > > > > Hi, > > > Does anyone know how to put an assertion in list comprehension? I have > > the following list comprehension, but I want to use an assertion to > > check the contents of rec_stdl. I ended up using another loop which > > essentially duplicates the functions of list comprehension. It just > > look like a waste of coding and computer time to me. > > > I just wish I could put the assertions into list comprehensions. > > > x=[(rec_stdl[0].st/10000.0, > > rec_stdl[0].cl, > > rec_stdl[0].bb, > > rec_stdl[0].bo, > > rec_stdl[1].bb, > > rec_stdl[1].bo, > > rec_stdl[0].ex > > ) > > for rec_stdl in rec_by_ex if len(rec_stdl)==2 > > ] > > > #duplicated loop > > if __debug__: > > for rec_stdl in rec_by_ex: > > l=len(rec_stdl) > > assert(l<=2 and l>0) > > if l==2: > > assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P") > > assert(rec_stdl[0].ex==rec_stdl[1].ex) > > assert(rec_stdl[0].st==rec_stdl[1].st) > > assert(rec_stdl[0].cp==rec_stdl[1].cp) > > First: All your asserts are wrong. Assert is a statement, not a > function. These specific ones will behave as expected, but it's easy > to accidentally write ones that always pass this way. Do you mean I should not use the parentheses? > Secondly: This is a waste of code, because if __debug__ is not defined > asserts will be skipped by the compiler. You could use the same loop > block for both branches. I know. My original question was how. Dan suggested to write a checker function. > Thirdly: This sort of testing is precisely what unit tests and/or > doctests are for. Agreed.

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calling a .net application from Python 2.5
by Acm Aug. 1, 2007

Aug. 1, 2007

I am working with Python 2.5. I would like to know how to call a .NET application (or .dll) from a Python script. Can anyone help please? Thank you.

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Time object?
by Robert Dailey Aug. 1, 2007

Aug. 1, 2007

Hi, I'm well aware of the datetime module, however it is really inconsistent and useless to me. In order to do any arithmetic on time objects, I have to use the 'timedelta' class, which doesn't even allow me to do all the math I want to do. For example, I want to do "1 / timeobj", where timeobj might represent a time in the format of "00:00:00.000000". Do I have to code my own class for this, or is there some other third party library out there that will allow me to do this? Thanks.

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Assertion in list comprehension
by beginner Aug. 1, 2007

Aug. 1, 2007

Hi, Does anyone know how to put an assertion in list comprehension? I have the following list comprehension, but I want to use an assertion to check the contents of rec_stdl. I ended up using another loop which essentially duplicates the functions of list comprehension. It just look like a waste of coding and computer time to me. I just wish I could put the assertions into list comprehensions. x=[(rec_stdl[0].st/10000.0, rec_stdl[0].cl, rec_stdl[0].bb, rec_stdl[0].bo, rec_stdl[1].bb, rec_stdl[1].bo, rec_stdl[0].ex ) for rec_stdl in rec_by_ex if len(rec_stdl)==2 ] #duplicated loop if __debug__: for rec_stdl in rec_by_ex: l=len(rec_stdl) assert(l<=2 and l>0) if l==2: assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P") assert(rec_stdl[0].ex==rec_stdl[1].ex) assert(rec_stdl[0].st==rec_stdl[1].st) assert(rec_stdl[0].cp==rec_stdl[1].cp) Thanks, Geoffrey

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Re: What is the "functional" way of doing this?
by Steven D'Aprano Aug. 1, 2007

Aug. 1, 2007

On Tue, 31 Jul 2007 09:01:42 -0300, Ricardo Aráoz wrote: > Considering I am a beginner I did a little test. Funny results too. The > function I proposed (lists1.py) took 11.4529998302 seconds, while the > other one (lists2.py) took 16.1410000324 seconds, thats about 40% more. > They were run in IDLE from their own windows (F5). [snip code] You may find that using the timeit module is better than rolling your own timer. >>> def recursive_func(n): ... if n > 0: ... return [n % 26] + recursive_func(n/26) ... else: ... return [] ... >>> def generator_func(n): ... def mseq(n): ... while n > 0: ... n, a = divmod(n, 26) ... yield a ... return list(mseq(n)) ... >>> >>> import timeit >>> N = 10**6+1 >>> timeit.Timer("recursive_func(N)", ... "from __main__ import N, recursive_func").repeat() [16.48972487449646, 17.000514984130859, 16.520529985427856] >>> >>> timeit.Timer("generator_func(N)", ... "from __main__ import N, generator_func").repeat() [27.938560009002686, 28.970781087875366, 23.977837085723877] If you're going to compare speeds, you should also test this one: >>> def procedural_func(n): ... results = [] ... while n > 0: ... n, a = divmod(n, 26) ... results.append(a) ... return results ... >>> >>> timeit.Timer("procedural_func(N)", ... "from __main__ import N, procedural_func").repeat() [15.577107906341553, 15.60145378112793, 15.345284938812256] I must admit that I'm surprised at how well the recursive version did, and how slow the generator-based version was. But I'd be careful about drawing grand conclusions about the general speed of recursion etc. in Python from this one single example. I think this is simply because the examples tried make so few recursive calls. Consider instead an example that makes a few more calls: >>> N = 26**100 + 1 >>> >>> timeit.Timer("recursive_func(N)", ... "from __main__ import N, recursive_func").repeat(3, 10000) [7.0015969276428223, 7.6065640449523926, 6.8495190143585205] >>> timeit.Timer("generator_func(N)", ... "from __main__ import N, generator_func").repeat(3, 10000) [3.56563401222229, 3.1132731437683105, 3.8274538516998291] >>> timeit.Timer("procedural_func(N)", ... "from __main__ import N, procedural_func").repeat(3, 10000) [3.3509068489074707, 4.0872640609741211, 3.3742849826812744] -- Steven.

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Re: Where do they tech Python officialy ?
by Ant Aug. 1, 2007

Aug. 1, 2007

On Aug 1, 9:40 am, Alex Popescu <nospam.themindst...(a)gmail.com> wrote: ... > It depends :-). In my experience I met employers being concerned by my > implication in the oss world :-). I have the opposite experience. It was predominantly the fact that I was involved in several open source projects that got me into professional development 3 years ago. The employers in the market at the time required 2 years+ of commercial experience - the fact that I was involved in OSS helped on two counts, firstly that it showed that I actually have an interest in development (rather than being another Comp Sci graduate just after a wage), and secondly that I have experience in good development practice (the open source projects I worked on had better infrastructure in place than two of the three companies I've worked for since!) -- Ant... http://antroy.blogspot.com/

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Problem with subprocess.Popen()
by The Cruisemaniac Aug. 1, 2007

Aug. 1, 2007

Hi all, I'm trying to run a windows batch file from a python script using subprocess.popen(). The issue that I'm facing is that, if i give the batch file as parameter to the popen function, the script runs, but if i provide a parameter, it is not working. Can someone help me with the command. The actual windows command to be executed is: test.bat -t ABC_DE_FG_HI_001 "C:\ABCDEFGHIJKLMNOP.TXT" What is the actual parameter required for subprocess.Popen(parameter chain) in this case?? Kindly help me out... Regards and Thanks in advance... Ashwin Murali.

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