A Hodgepodge of Python

Re:A Hodgepodge of Python by lysium on Thursday September 15, 2011 @05:15PM (#3002164)

Didn't know the timeit module. However, the presented usage to time list reversing is ill: The timing is dominated by the list creation, which should go into setup. Then I'll get:

    $ python -mtimeit -s'l=range(1000)' 'l[::-1]'      
    100000 loops, best of 3: 3.05 usec per loop
    $ python -mtimeit -s'l=range(1000)' 'l.reverse()'  
    1000000 loops, best of 3: 0.535 usec per loop
    $ python -mtimeit -s'l=range(1000)' 'a=reversed(l)' 
    1000000 loops, best of 3: 0.39 usec per loop

So, instead of reversing the list in place, creating a new, reversed list seems to be faster.

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Re:A Hodgepodge of Python by Sharlin on Thursday September 15, 2011 @05:40PM (#3002235)

  >>> reversed([])
  <listreverseiterator object at 0xb73ff7cc>

reversed() does not create a new list, it just returns a reverse-order view of the same list. Of course, often this is exactly what is needed.

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Re:A Hodgepodge of Python by akx on Friday September 16, 2011 @06:17AM (#3003886)

And more often than not `xrange` is what one needs, not `range`. (Not relevant with Py3k though, but everyone is still in 2.x-verse.)

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Re:A Hodgepodge of Python by lysium on Friday September 16, 2011 @08:09AM (#3004115)

    >>> xrange(13)[::-1]
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: sequence index must be integer, not 'slice'

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Re:A Hodgepodge of Python by akx on Friday September 16, 2011 @09:15AM (#3004295)

  >>> list(range(13)[::-1]) == list(xrange(12, -1, -1))
  True

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Re:A Hodgepodge of Python by lysium on Friday September 16, 2011 @08:08AM (#3004112)

True: $ python -mtimeit -s'l=range(1000)' 'a=[i for i in reversed(l)]' 10000 loops, best of 3: 37.7 usec per loop

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