List Comprehension

List comprehensions are used to derive a new list from an existing list. For example, you have a list of
numbers and you want to get a corresponding list with all the numbers multiplied by 2 but only when the
number itself is greater than 2. List comprehensions are ideal for such situations.
Using List Comprehensions

Example 15.1. Using List Comprehensions
#!/usr/bin/python
# Filename: list_comprehension.py
listone = [2, 3, 4]
listtwo = [2*i for i in listone if i > 2]
print listtwo

Output
$ python list_comprehension.py
[6, 8]


How It Works
Here, we derive a new list by specifying the manipulation to be done (2*i) when some condition is satisfied
(if i > 2). Note that the original list remains unmodified. Many a time, we use loops to process
each element of a list, the same can be achieved using list comprehensions in a more precise, compact
and explicit manner.