Dustan <[EMAIL PROTECTED]> wrote: > On May 5, 3:15 am, kaens <[EMAIL PROTECTED]> wrote: > > I think the for i in range() is more readable (Maybe because I'm > > coming from a c-style syntax language background) - but what would > > the benefits of using enumerate be (other that being more . . . > > pythonesque?) > > It doesn't create a whole new list just for iterating.
As the example list was of length 5, that's not all that important in this case. In cases where it _is_ crucial, you can use xrange. The performance of the various ways of looping is substantially the same: $ python -mtimeit -s'n=5; a=n*[23]' 'for i in range(n): x=a[i]' 1000000 loops, best of 3: 1.4 usec per loop $ python -mtimeit -s'n=5; a=n*[23]' 'for i in xrange(n): x=a[i]' 1000000 loops, best of 3: 1.18 usec per loop $ python -mtimeit -s'n=5; a=n*[23]' 'for i,v in enumerate(a): x=v' 1000000 loops, best of 3: 1.49 usec per loop $ Here, xrange is minutely faster and enumerate slower, but each speed difference "in the noise". Focusing on clarity is thus well warranted. > > > > for i in range(n): > > > > for j in range(i+1, n): > > > > print a[i], a[j] > > > > > Ah, but wouldn't the cleaner Python be something like > > > > > >>> a = [1, 2, 3, 4, 5, 3, 6] #just to confuse matters > > > >>> for pos, val in enumerate(a): > > > ... for v2 in a[pos+1:]: > > > ... print val, v2 This "breaks symmetry", by using enumerate in the outer loop and a slice in the inner loop; the symmetrical construction of using range in both loops is a big conceptual/clarity win -- the reader of the code needs to "grasp" one fewer concept (locally). Using xrange in both loops would be just as good from this POV. Alex -- http://mail.python.org/mailman/listinfo/python-list
