The map() function is there to apply the same procedure to every item in an iterable data structure, like lists, generators, strings, and other stuff.
Let's look at an example:
map() can iterate over every item in a list and apply a function to each item, than it will return (give you back) the new list.
Imagine you have a function that takes a number, adds 1 to that number and returns it:
def add_one(num):
new_num = num + 1
return new_num
You also have a list of numbers:
my_list = [1, 3, 6, 7, 8, 10]
if you want to increment every number in the list, you can do the following:
>>> map(add_one, my_list)
[2, 4, 7, 8, 9, 11]
Note: At minimum map() needs two arguments. First a function name and second something like a list.
Let's see some other cool things map() can do.
map() can take multiple iterables (lists, strings, etc.) and pass an element from each iterable to a function as an argument.
We have three lists:
list_one = [1, 2, 3, 4, 5]
list_two = [11, 12, 13, 14, 15]
list_three = [21, 22, 23, 24, 25]
map() can make you a new list that holds the addition of elements at a specific index.
Now remember map(), needs a function. This time we'll use the builtin sum() function. Running map() gives the following result:
>>> map(sum, list_one, list_two, list_three)
[33, 36, 39, 42, 45]
REMEMBER:
In Python 2 map(), will iterate (go through the elements of the lists) according to the longest list, and pass None to the function for the shorter lists, so your function should look for None and handle them, otherwise you will get errors. In Python 3 map() will stop after finishing with the shortest list. Also, in Python 3, map() returns an iterator, not a list.