Format string: add more fast-path

[vstinner]

BPO	15609
Nosy	@pitrou, @vstinner
Files	optimize_format.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2012-10-01.22:44:22.947>
created_at = <Date 2012-08-09.20:01:46.200>
labels = ['performance']
title = 'Format string: add more fast-path'
updated_at = <Date 2012-10-02.10:54:15.013>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2012-10-02.10:54:15.013>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2012-10-01.22:44:22.947>
closer = 'vstinner'
components = []
creation = <Date 2012-08-09.20:01:46.200>
creator = 'vstinner'
dependencies = []
files = ['26749']
hgrepos = []
issue_num = 15609
keywords = ['patch']
message_count = 3.0
messages = ['167827', '171754', '171784']
nosy_count = 3.0
nosy_names = ['pitrou', 'vstinner', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue15609'
versions = ['Python 3.4']

[vstinner]

Attached patch adds tests to check that str%args and str.format(args) take all optimization opportunities for simple format strings. It takes also the fast-path when Unicode string argument when width and/or precision is set. For example, "%.3s" % "abc" now returns "abc" unmodified (instead of creating a copy). The patch also takes the fast-path when formatting integers with str%args when the argument is not an int, but an object with __int__ method.

[python-dev]

New changeset 559a430e563c by Victor Stinner in branch 'default':
Issue bpo-15609: Optimize str%args for integer argument
http://hg.python.org/cpython/rev/559a430e563c

[python-dev]

New changeset 5ddc7b3f2795 by Victor Stinner in branch 'default':
Issue bpo-15609: Fix refleak introduced by my last optimization
http://hg.python.org/cpython/rev/5ddc7b3f2795