Map
Maps
First: What is 'map'?
In very short, map
runs the given function over the given iterable.
For example: We have a function that converts years to their Roman numeral version. And we have a list of years. We can run a map(convert_year_to_roman_numeral, ['1999', '1776', '2015']
. This will run the function convert_year_to_roman_numeral
on the list of years. And return the Roman numerals for those years. As a list.
The Syntax
map(function, iterable)

The function can be a function or a lambda expression.

The iterable can be any iterable  list, string, etc.
A few examples:
map(lambda x: x**2, [1, 2, 3, 4])
 The function here is a lambda.
 The iterable is the list.
 This runs the lambda (x**2) on the first item in the iterable  on the
1
.  Then runs the lambda on the next item in the iterable, and so on. Until all items have been run.
 The result is
[1, 4, 9, 16]
def sqr(num):
return num **2
seq = [1, 2, 3, 4]
map(sqr,seq)
 This runs exactly as above.
 It runs the
sqr
function on theseq
. And run the function on every item in the iterable.