[issue14744] Use _PyUnicodeWriter API in str.format() internals

[STINNER Victor]

STINNER Victor <victor.stinner at gmail.com> added the comment:

For Python 3.3, _PyUnicodeWriter API is faster than the Py_UCS4 buffer API and PyAccu API in quite all cases, with a speedup between 30% and 100%. But there are some cases where the _PyUnicodeWriter API is slower:

fmt="x={}"; arg=12.345; fmt.format(arg)
fmt="{}:"; arg=12.345; fmt.format(arg)
fmt="x=%s"; arg="\u20ac" * 3; fmt % arg
fmt="%s:"; arg="abc"; fmt % arg
fmt="%s:"; arg="\u20ac" * 3; fmt % arg
fmt="\u20ac[%s]"; arg="abc"; fmt % arg
fmt="\u20ac[%s]"; arg="\u20ac" * 3; fmt % arg
fmt="\u20ac[%s]"; arg=12.345; fmt % arg
fmt="\u20ac[%s]"; arg=2j; fmt % arg

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue14744>
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