30.10.17 12:10, Kirill Balunov пише:
Sometime ago I asked this question at SO [1], and among the responses
received was paragraph:
- `zip` re-uses the returned `tuple` if it has a reference count of 1 when
the `__next__` call is made.
- `map` build a new `tuple` that is passed to the mapped function every
time a `__next__` call is made.
Why can not `map` use the same approach as `zip`?
Also it turns out that a faster solution looks not reasonable, since it
requires additional calculations..
[1] https://stackoverflow.com/questions/46172018/perfomance-
of-map-vs-starmap
Sometime ago I had wrote a sample patch for using cached arg tuples in
map() and several other functions [1]. It increased the speed in
microbenchmarks up to 24-38%. But the code was too complex and fragile,
I didn't want to commit it. Later, after numerous of attempts, this
resulted in implementing by Victor Stinner the new private "fastcall"
calling method which allowed to avoid creation a new tuple (and a dict
for keyword arguments) in many cases. It was added just before releasing
of 3.6 and was used in few places. In 3.7 it was optimized further. Now
map() is faster than starmap()+zip().
Python 3.6:
$ ./python -m timeit -s 'from operator import eq; from itertools import
starmap; seq1 = [1]*1; seq2 = [1]*1' 'list(map(eq, seq1, seq2))'
1000 loops, best of 3: 559 usec per loop
$ ./python -m timeit -s 'from operator import eq; from itertools import
starmap; seq1 = [1]*1; seq2 = [1]*1' 'list(starmap(eq, zip(seq1,
seq2)))'
1000 loops, best of 3: 399 usec per loop
Python 3.7:
$ ./python -m timeit -s 'from operator import eq; from itertools import
starmap; seq1 = [1]*1; seq2 = [1]*1' 'list(map(eq, seq1, seq2))'
1000 loops, best of 5: 338 usec per loop
$ ./python -m timeit -s 'from operator import eq; from itertools import
starmap; seq1 = [1]*1; seq2 = [1]*1' 'list(starmap(eq, zip(seq1,
seq2)))'
1000 loops, best of 5: 359 usec per loop
[1] https://bugs.python.org/issue23507
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