🌐 Mailman 3 December 2009 - Python-list - python.org

Re: python for loop
by Steven D'Aprano July 10, 2013

July 10, 2013

On Wed, 01 Apr 2009 04:39:26 +0100, Rhodri James wrote: > Dragging this back to the original topic, you clearly find starting list > indices from zero unintuitive. To me, with a mathematical background, > it's not just intuitive, it's correct. All sorts of useful properties > fall out from that, not the least of which is the fact that > "a[0:len(a)]" slices the whole of a list. But some non-useful properties fall out of that too. Want the fifth item? a[5] gives you the *sixth* item, which is weird, so you have to use a[5-1] to get the fifth item. There is a major clash between the names of ordinals in human languages and zero-based counting. In human languages, the Nth-ordinal item comes in position N. You can keep that useful convention with zero-based counting by inventing the ugly word "zeroth", but that just leads to bizarro-talk like "the zeroeth item comes first, the first item comes second, and so on". a[0:len(a)] is legal, a[0] is legal, but surprisingly a[len(a)] is an error. Despite coming from a Pascal background, I've come to appreciate and prefer zero-based indexing for programming. But I'm not blind to the disadvantages. I'll often work out an algorithm using pencil and paper and counting from one, and then subtract one to get zero-based indexes. There are advantages and disadvantages to both systems, but on balance, I think that zero-based is a better system for programming, and one-based for natural language. -- Steven

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Coping with cyclic imports
by Torsten Bronger July 6, 2013

July 6, 2013

Hallöchen! I have a rather fat module that represents a document parser -- inline elements, block elements, and the like. Now I want to split it into many modules to make everything more manageable. But at the moment I don't see how to avoid cyclic imports: A document element A, which is represented my module parser.A, may contain the element B, as defined in parser.B. And vice versa. So both modules must import each other, as far as I can see. I know that cyclic imports work in Python under certain circumstances. Can anyone refer me to a page which explains *when* this works? Because at least once, the imported module was not "finished" and thus largely unusual. Thank you! Tschö, Torsten. -- Torsten Bronger, aquisgrana, europa vetus Jabber ID: bronger(a)jabber.org (See http://ime.webhop.org for further contact info.)

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June 12, 2013

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global variable not working inside function. Increment
by Helvin May 13, 2013

May 13, 2013

Hi, This increment thing is driving me nearly to the nuts-stage. > < I have a function that allows me to pick points. I want to count the number of times I have picked points. global no_picked no_picked = 0 def picked(object, event): no_picked += 1 print no_picked Error msg says: UnboundLocalError: local variable 'no_picked' referenced before assignment For some reason, no_picked does not increment, but the printing statement works. Do you know why? (I'm actually writing this for a vtkrenderwindowinteractor.) Helvin

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how to get next month string?
by Yinghe Chen May 2, 2013

May 2, 2013

Hi, Could someone help on how to use python to output the next month string like this? "AUG07", suppose now is July 2007. I think also need to consider Dec 07 case, it is supposed to output as below: "JAN07". datetime module seems not supporting the arithmatic operations, any hints? Thanks in advance, Yinghe Chen

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Calling J from Python
by Gosi March 9, 2013

March 9, 2013

It is quite easy to call J from Python http://groups.google.com/group/J-Programming/browse_thread/thread/5e84b7566…

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Re: problems trying to build python 2.6 as a shared library
by Marco Nawijn Jan. 19, 2013

Jan. 19, 2013

On Sep 25, 1:08 pm, Chris Withers <ch...(a)simplistix.co.uk> wrote: > Hi All, > > I'm trying to build Python 2.6 as a shared library, so I did: > > ./configure --enable-shared > make > make altinstall > > No obvious signs of failure, but when I try and use the resulting > python, I get: > > python2.6: error while loading shared libraries: libpython2.6.so.1.0: > cannot open shared object file: No such file or directory > > Why might that be? > > cheers, > > Chris > > -- > Simplistix - Content Management, Batch Processing & Python Consulting > -http://www.simplistix.co.uk Hello Chris, The dynamic loader cannot find the python shared library. There are at least 2 options: 1. Add path that contains the shared library to the LD_LIBRARY_PATH environment variable. In a bash shell this can be accomplished by: export LD_LIBRARY_PATH=/path/to/python_shared_lib: $LD_LIBRARY_PATH 2. Add path to dynamic linker configuration file. This typically is in '/etc/ld.so.conf'. See man page for ld for more information. Note that I assumed that you are on a Unix/Linux machine. Regards, Marco

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Weirdness with python and stdin redirection under Win32
by Jonathan M. Gilligan Jan. 18, 2013

Jan. 18, 2013

I am getting an error reading stdin only when I invoke a python script by typing "bar | foo.py" or "foo.py < bar", but not when typing "bar | python foo.py" or "python foo.py < bar". The error arises ecause when input is redirected, stdin has fileno = -1 if the script is invoked as "foo.py", but correctly has fileno = 0 if it is invoked as "python foo.py" Consider the following script, which I want to use as a prototype for a simple stdin --> stdout filter: # foo.py import sys print "fileno = ", sys.stdin.fileno() lines = sys.stdin.xreadlines() for line in lines: sys.stdout.write(line) On win32 (Win2k pro, SP3), using ActiveState ActivePython 2.2.1 build 222, I can execute foo.py either by typing "foo.py" or "python foo.py" on the command line (the relevant registry key for opening .py files has command 'C:\Python22\python.exe "%1" %*'). If I type "echo bar | foo.py", I get C:\>echo bar | foo.py The process tried to write to a nonexistent pipe. fileno = -1 Traceback (most recent call last): File "C:\foo.py", line 7, in ? lines = sys.stdin.readlines() IOError: [Errno 9] Bad file descriptor whereas if I type "echo bar | python foo.py", I get C:\>echo bar | python foo.py fileno = 0 bar Other tests yield: C:\>foo.py < foo.py fileno = -1 Traceback (most recent call last): File "C:\Documents and Settings\Jonathan\My Documents\Programming\Omap VU\Fast CameraDriver\BF_LabView\Leo\foo.py", line 7, in ? for line in lines: IOError: [Errno 9] Bad file descriptor C:\>python foo.py < foo.py fileno = 0 # foo.py import sys print "fileno = ", sys.stdin.fileno() lines = sys.stdin.xreadlines() for line in lines: sys.stdout.write(line) If I just type "foo.py" or "python foo.py" on the command line, I get "fileno = 0" in both cases and the script works identically in both cases. Can anyone explain what's happening? Why the file descriptor for redirected stdin has a fileno of -1 if the python script is invoked using "foo.py" but not when it's invoked with "python foo.py"? Thanks, Jonathan

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PHP vs. Python
by stephen.mayer＠gmail.com Sept. 25, 2012

Sept. 25, 2012

Anyone know which is faster? I'm a PHP programmer but considering getting into Python ... did searches on Google but didn't turn much up on this. Thanks! Stephen

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