The map() function

The map function (seen in Bar Graph) can simplify some list processing. The command,

map(fn, seq)

builds a new list from an existing one by applying the function fn to every member of the sequence seq. For example if you have the list of strings, names = ['Tim', 'Mary', 'Stephanie', 'Bob'], and want a list of the lengths of those strings map is just the ticket. It creates a map object that can be cast to a list:

>>> names = ['Tim', 'Mary', 'Stephanie', 'Bob']
>>> len_list = map(len, names)
>>> list(len_list)
[3, 4, 9, 3]
>>> 

map doesn't do anything magical it just replaces the loop construction,

len_list = []
for item in names:
    len_list.append(len(item))

with a more compact, and less error-prone notation.

Some languages don't provide a map function in which case you may want to write your own¹] since it's so handy.