[Python-Dev] Usage of += on strings in loops in stdlib (original) (raw)
Steven D'Aprano steve at pearwood.info
Thu Feb 14 01:25:58 CET 2013
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On 14/02/13 01:18, Chris Withers wrote:
On 13/02/2013 11:53, Steven D'Aprano wrote:
I fixed a performance bug in httplib some years ago by doing the exact opposite; += -> ''.join(). In that case, it changed downloading a file from 20 minutes to 3 seconds. That was likely on Python 2.5.
I remember it well. http://mail.python.org/pipermail/python-dev/2009-August/091125.html I frequently link to this thread as an example of just how bad repeated string concatenation can be, how painful it can be to debug, and how even when the optimization is fast on one system, it may fail and be slow on another system. Amusing is that http://mail.python.org/pipermail/python-dev/2009-August/thread.html#91125 doesn't even list the email where I found the problem...
That's because it wasn't solved until the following month.
http://mail.python.org/pipermail/python-dev/2009-September/thread.html#91581
-- Steven
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