[issue23493] optimize sort_keys in json module by using operator.itemgetter()

[Wouter Bolsterlee]

Wouter Bolsterlee added the comment:

Using IPython and CPython 3.4:

>>> d = dict.fromkeys(map(str, range(1000)))


Current implementation:

>>> %timeit sorted(d.items(), key=lambda kv: kv[0])
1000 loops, best of 3: 605 µs per loop
>>> %timeit sorted(d.items(), key=lambda kv: kv[0])
1000 loops, best of 3: 614 µs per loop

Proposed change:

>>> %timeit sorted(d.items(), key=operator.itemgetter(0))
1000 loops, best of 3: 527 µs per loop
>>> %timeit sorted(d.items(), key=operator.itemgetter(0))
1000 loops, best of 3: 523 µs per loop

Alternative without 'key' arg, since all keys in a JSON object must be strings, so the tuples from .items() can be compared directly.:

>>> %timeit sorted(d.items())
1000 loops, best of 3: 755 µs per loop
>>> %timeit sorted(d.items())
1000 loops, best of 3: 756 µs per loop

As you can see, the operator approach seems the fastest on CPython 3.4, even faster than not having a 'key' arg at all (possibly because it avoids doing a tuple compare, which descends into a string compare for the first item).

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23493>
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