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Sat Oct 25 17:18:42 EDT 2003 · https://mail.python.org/pipermail/python-dev/2003-October/039511.html

> Modified Files:
>       Tag: release23-maint
> 	bltinmodule.c 
> Log Message:
> changed builtin_sum to use PyNumber_InPlaceAdd -- unchanged semantics but
> fixes performance bug with sum(lotsoflists, []).

I think this ought to be reverted, both in 2.3 and 2.4.  Consider this code:

empty = []
for i in range(10):
  print sum([[x] for x in range(i)], empty)

The output used to be:

[]
[0]
[0, 1]
[0, 1, 2]
[0, 1, 2, 3]
[0, 1, 2, 3, 4]
[0, 1, 2, 3, 4, 5]
[0, 1, 2, 3, 4, 5, 6]
[0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 2, 3, 4, 5, 6, 7, 8]

But now it is:

[]
[0]
[0, 0, 1]
[0, 0, 1, 0, 1, 2]
[0, 0, 1, 0, 1, 2, 0, 1, 2, 3]
[0, 0, 1, 0, 1, 2, 0, 1, 2, 3, 0, 1, 2, 3, 4]
[0, 0, 1, 0, 1, 2, 0, 1, 2, 3, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 5]
[0, 0, 1, 0, 1, 2, 0, 1, 2, 3, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6]
[0, 0, 1, 0, 1, 2, 0, 1, 2, 3, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 7]
[0, 0, 1, 0, 1, 2, 0, 1, 2, 3, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7, 8]

--Guido van Rossum (home page: http://www.python.org/~guido/)

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Showing content from https://mail.python.org/pipermail/python-dev/2003-October/039511.html below:

[Python-checkins] python/dist/src/Python bltinmodule.c, 2.292.10.1, 2.292.10.2