As mentioned in Section 3.6, Python's for loops are actually foreach loops: for each element in the list that follows, repeat the nested block that follows the for statement, e.g.
>>> for i in 1,2,3,4: print i 1 2 3 4
This is fundamentally different to the way
for loops work in
other languages. It allows the index of the for loop (
i in this
example to step through arbitrary elements.
By using the range function we are replicating the behaviour of
for loops in most other languages (C, Pascal, etc.). That is
the index is implemented by a constant amount between an lower and
However, in Python for loops are much more flexible. Consider the following example:
>>> for i in 1,2,3,500: print i 1 2 3 500
This kind of thing is not easy to do in other languages.
for loop usually steps through a list of items, but it can
also be used with arrays:
>>> from Numeric import * >>> xx = array([1,10.2,-509]) >>> for i in xx: print i 1.0 10.2 -509.0
This is very useful when writing functions which take array parameters whose size is not known in advance.