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Date: Sat, 9 Feb 2013 11:05:54 +1100
Subject: Re: Implicit conversion to boolean in if and while statements
From: Chris Angelico <rosuav@gmail.com>
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Xref: csiph.com comp.lang.python:38481

On Sat, Feb 9, 2013 at 6:58 AM, Rick Johnson
<rantingrickjohnson@gmail.com> wrote:
> I'm a bit unnerved by the sum function. Summing a sequence only makes sen=
se if the sequence in question contains /only/ numeric types. For that reas=
on i decided to create a special type for holding Numerics. This will proba=
bly result in many complaints from lazy people who want to use only one Seq=
uence type, which holds mixed types, THEN jamb nothing but numeric types in=
to it, THEN have a sum method that throws errors when it encounters a non-n=
umeric type!!! I say, too bad for you.


Most assuredly not. The sum builtin works happily on any sequence of
objects that can be added together. It works as an excellent flatten()
method:

>>> nested_list =3D [["q"], ["w","e"], ["r","t","u"], ["i","o","p"]]
>>> sum(nested_list,[])
['q', 'w', 'e', 'r', 't', 'u', 'i', 'o', 'p']
>>> nested_list
[['q'], ['w', 'e'], ['r', 't', 'u'], ['i', 'o', 'p']]

I'm not sure what your definition of a numeric type is, but I suspect
that list(str) isn't part of it.

ChrisA