restriction on sum: intentional bug?  Stephen Hansen apt.shansen
at Fri Oct 16 18:00:29 CEST 2009  On Fri, Oct 16, 2009 at 8:39
AM, Alan G Isaac <alan.isaac at> wrote:  > I expected this to be
fixed in Python 3: >  sum(['ab','cd'],'') >>> Traceback (most
recent call last): > TypeError: sum() can't sum strings [use
''.join(seq) instead] > Of course it is not a good way to join
strings, > but it should work, should it not?  Naturally, >  ''
+ 'ab' + 'cd' >>> 'abcd' > Why doesn't duck typing apply to
`sum`? Because it would be so hideously slow and inefficient
that it'd be way too easy a way for people to program something
they think should work fine but really doesn't... alternatively,
the function would have to do two /completely/ different
implementations based on what you're passing in, and that
violates duck typing too :)  Duck typing isn't an absolute.
Sum's not broken... This is a "practicality beats purity" thing;
maybe sum should just add up everything passed to it and as long
as no errors happen, retur