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(python2.1-tut.info)range Function

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The `range()' Function
======================

If you do need to iterate over a sequence of numbers, the built-in
function `range()' comes in handy.  It generates lists containing
arithmetic progressions, e.g.:

     >>> range(10)
     [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

The given end point is never part of the generated list; `range(10)'
generates a list of 10 values, exactly the legal indices for items of a
sequence of length 10.  It is possible to let the range start at
another number, or to specify a different increment (even negative;
sometimes this is called the `step'):

     >>> range(5, 10)
     [5, 6, 7, 8, 9]
     >>> range(0, 10, 3)
     [0, 3, 6, 9]
     >>> range(-10, -100, -30)
     [-10, -40, -70]

To iterate over the indices of a sequence, combine `range()' and
`len()' as follows:

     >>> a = ['Mary', 'had', 'a', 'little', 'lamb']
     >>> for i in range(len(a)):
     ...     print i, a[i]
     ...
     0 Mary
     1 had
     2 a
     3 little
     4 lamb