This document discusses Python list comprehensions as a more concise way to construct lists compared to traditional for loops. It provides an example of constructing a list of squares of even numbers using a for loop that appends to an empty list, and compares it to using a list comprehension with the same condition in one line. The list comprehension approach is described as cleaner and faster than the traditional method.

1. Python List
Comprehensions

2. ‘Traditional’ way
Constructing a list of squares of even numbers:
squares_of_evens = []
# range(10) -> [0,1,2,3,4,5,6,7,8,9]
for n in range(10):
if n%2==0:
squares_of_evens.append(n*n)
print squares_of_evens #[0, 4, 16, 36, 64]
It works - but ugly and slow!

3. Construct lists in a concise way
General syntax:
new_list = [new_item for item in input_list]
new_list = [new_item for item in input_list if some_condition]
Squares of even numbers:
squares_of_evens = [n*n for n in range(10) if (n%2 == 0)]
print squares_of_evens #[0, 4, 16, 36, 64]

4. Thanks!