[Patches] [ python-Patches-724936 ] new sum builtin

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Patches item #724936, was opened at 2003-04-21 06:33
Message generated for change (Comment added) made by gvanrossum
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Category: Core (C code)
Group: Python 2.3
Status: Open
Resolution: None
Priority: 7
Submitted By: Alex Martelli (aleax)
Assigned to: Guido van Rossum (gvanrossum)
Summary: new sum builtin

Initial Comment:
as per discussion on Python-Dev.  Note that 
sum(manystrings), while still FAR faster than 
reduce(operator.add, manystrings) and the equivalent loop, 
is now about twice as slow as ''.join(manystrings) -- to 
support  the possibility that "manystrings" may be an 
iterator, sum must retain the first item and 
string-concatenate to it the ''.join of the others.  I have not 
mentioned this slight performance hit in the docs (just as 
the far more severe performance trap with 
reduce(operator.add, manystrings) is nowhere mentioned).  
Also, I have not edited the tutorial.  Please let me know if 
you want more editing of such docs, I'll be quite glad to do 
it, of course!


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>Comment By: Guido van Rossum (gvanrossum)
Date: 2003-04-21 11:52

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I thought we would allow a second argument specifying the
starting point, defaulting to 0 (so w is never NULL).  See
my pseudo code posted to python-dev. (Except if it used +=,
ignore that.)

Also, I would refrain from mentioning lists or tuples in the
docs, since those in fact have the same O(N**2) behavior as
strings. better use datetime.timedelta as the example.

What would you suggest to modify in the tutorial?  Does it
even mention reduce()?

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Comment By: Alex Martelli (aleax)
Date: 2003-04-21 11:44

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modified as per GvR's pronouncement on python-dev: now 
sum([]) returns 0, and it's specifically forbidden for the first item of 
the argument to be a string (a TypeError is raised and the 
message tells the user to use ''.join instead).  Guido, please do let 
me know if I should edit the tutorial as well, thanks!


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Comment By: Guido van Rossum (gvanrossum)
Date: 2003-04-21 08:21

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I have to rethink the idea that sum() should only apply to
numbers. The discussion brought up some new good points that
I need to ponder.

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