Giovanni Bajo wrote: > I found this strange: > > python -mtimeit "sum(int(L) for L in xrange(3000))" > 100 loops, best of 3: 5.04 msec per loop > > python -mtimeit "import itertools; sum(itertools.imap(int, xrange(3000)))" > 100 loops, best of 3: 3.6 msec per loop > > I thought the two constructs could achieve the same speed.
I think early binding would have been preferable, but as Fredrik Lundh said, int is looked up for every iteration which accounts for the slowdown. For reference: $ python -m timeit "sum(int(i) for i in xrange(3000))" 1000 loops, best of 3: 1.92 msec per loop $ python -m timeit -s "from itertools import imap" "sum(imap(int, xrange(3000)))" 1000 loops, best of 3: 1.17 msec per loop You can shave off a few percent by turning int into a local variable: $ python -m timeit -s "int_ = int" "sum(int_(i) for i in xrange(3000))" 1000 loops, best of 3: 1.74 msec per loop On the other hand the function call overhead that imap() sometimes enforces is larger than the cost of a symbol lookup: $ python -m timeit -s"def square(i): return i*i" -s"from itertools import imap" "sum(imap(square, xrange(3000)))" 100 loops, best of 3: 2.25 msec per loop $ python -m timeit "sum(i*i for i in xrange(3000))" 1000 loops, best of 3: 1.29 msec per loop Peter -- http://mail.python.org/mailman/listinfo/python-list
