Python List Comprehensions
1 like627 views
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 of 4
Downloaded 15 times
![‘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!](https://image.slidesharecdn.com/growbeyondwithgooglepres-160922044205/85/Python-List-Comprehensions-2-320.jpg)
![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]](https://image.slidesharecdn.com/growbeyondwithgooglepres-160922044205/85/Python-List-Comprehensions-3-320.jpg)
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!