Python Essential Reference, Second Edition

map(), zip(), reduce(), and filter()

The t = map(func , s ) function applies the function func to each of the elements in s and returns a new list t . Each element of t is t [i ] = func(s [i ]). The function given to map() should require only one argument. For example:

a = [1, 2, 3, 4, 5, 6] 
def foo(x): 
    return 3*x 

b = map(foo,a)   # b = [3, 6, 9, 12, 15, 18] 

Alternatively, this could be calculated using an anonymous function as follows:

b = map(lambda x: 3*x, a)   # b = [3, 6, 9, 12, 15, 18] 

The map() function can also be applied to multiple lists such as t = map(func , s1 , s2 , ..., sn ). In this case, each element of t is t [i ] = func s1 [i ], s2 [i ], ..., sn [i ]), and the function given to map() must accept the same number of arguments ...