List Comprehensions in Python

List comprehensions provide a concise way to create lists.

It consists of brackets containing an expression followed by a for clause, then zero or more for or if clauses. The expressions can be anything, meaning you can put in all kinds of objects in lists.

The result will be a new list resulting from evaluating the expression in the context of the for and if clauses which follow it.

The list comprehension always returns a result list.

you can convert from:

new_list = []
for i in old_list:
    if filter(i):
        new_list.append(expressions(i))

into:

new_list = [expression(i) for i in old_list if filter(i)]

Here’s the break down:
new_list
The new list (result).

expression(i)
Expression is based on the variable used for each element in the old list.

for i in old_list
The word for followed by the variable name to use, followed by the word in the old list.

if filter(i)
Apply a filter with an If-statement.