How to create list with List Comprehension

What is List Comprehension

List comprehension is a way of making lists from other lists. It works in a way similar to for loops.

print [x*x for x in range(10)] 

The code above generates the following result.

The code above composes x*x for each x in range(10).

The following code prints out squares that are divisible by 3.

print [x*x for x in range(10) if x % 3 == 0] 

The code above generates the following result.

We can also create list of tuples.

print [(x, y) for x in range(3) for y in range(3)] 

The code above generates the following result.

This can be combined with an if clause.

firstList = ['abc', 'bcd', 'cde'] 
secondList = ['cde', 'abc', 'bcd'] 
print [b + ':' + g for b in firstList for g in secondList if b[0] == g[0]] 

This gives the pairs of boys and girls who have the same initial letter in their first name.

numbers = [72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100, 33]
print [chr(n) for n in numbers] # characters corresponding to numbers 
print [ord(c) for c in 'Hello, world!'] # numbers corresponding to characters 
print [n for n in numbers if n % 2 == 0] # filters out the odd numbers 
#   www.  j  a  v  a2 s  .  c  o  m

The code above generates the following result.