Python Essential Reference, Second Edition

Loops

The simple loops shown earlier used the while statement. The other looping construct is the for statement, which iterates over the members of a sequence, such as a string, list, or tuple. Here’s an example:

for i in range(1,10): 
        print "2 to the %d power is %d" % (i, 2**i) 

The range(i ,j ) function constructs a list of integers with values from i to j-1 . If the starting value is omitted, it’s taken to be zero. An optional stride can also be given as a third argument. For example:

a = range(5)         # a = [0,1,2,3,4] 
b = range(1,8)       # b = [1,2,3,4,5,6,7] 
c = range(0,14,3)    # c = [0,3,6,9,12] 
d = range(8,1,-1)    # d = [8,7,6,5,4,3,2] 

The for statement can iterate over any sequence type and isn’t limited to sequences of integers:

 a = "Hello World" ...