[issue6688] Optimize PyBytes_FromObject.

[Alexandre Vassalotti]

New submission from Alexandre Vassalotti <alexandre at peadrop.com>:

Optimize PyBytes_FromObject by adding special-cases for list and tuple
objects and by using _PyObject_LengthHint() instead of an arbitrary
value for the size of the initial buffer.

[Without the patch]
./python -m timeit -s "x = list(range(256))" "bytes(x)"
100000 loops, best of 3: 7.19 usec per loop

./python -m timeit -s "x = tuple(range(256))" "bytes(x)"
100000 loops, best of 3: 7.14 usec per loop

./python -m timeit -s "x = list(range(256))*100" "bytes(x)"
1000 loops, best of 3: 591 usec per loop

./python -m timeit -s "x = range(256)" "bytes(x)"
100000 loops, best of 3: 8.45 usec per loop


[With the patch]

./python -m timeit -s "x = list(range(256))" "bytes(x)"
100000 loops, best of 3: 4.43 usec per loop

./python -m timeit -s "x = tuple(range(256))" "bytes(x)"
100000 loops, best of 3: 4.53 usec per loop

./python -m timeit -s "x = list(range(256))*100" "bytes(x)"
1000 loops, best of 3: 335 usec per loop

./python -m timeit -s "x = range(256)" "bytes(x)"
100000 loops, best of 3: 7.56 usec per loop

----------
components: Interpreter Core
files: optimize_bytes_from_object.diff
keywords: patch
messages: 91486
nosy: alexandre.vassalotti
priority: normal
severity: normal
stage: patch review
status: open
title: Optimize PyBytes_FromObject.
type: performance
Added file: http://bugs.python.org/file14694/optimize_bytes_from_object.diff

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue6688>
_______________________________________