What is list comprehension in Python?

List comprehensions are a concise way to create lists. They are used to create a new list by iterating over another list.

Syntax

It consists of square brackets containing an expression followed by the “for” keyword. The result will be a list whose results match the expression.

The basic syntax is :

newlist = [output_expression(x) for x in oldlist if conditional(x)]

The above syntax is explained through the illustration below:

Parameters

The list comprehension basically consists of four parameters.

• Output expression: Defines the output of the list
• Oldlist: Defines the list which is to be traversed
• Conditional/predicate: Defines a condition on variable x. This is an optional parameter.
• Newlist: Save the result of list expression in the newlist

Example 1

The following code creates a list containing the square of numbers:

Example 2

The following code uses a predicate expression and stores only the square of those numbers in the list which is divisible by 2: