List Comprehensions

Say, there is a list, doctor = ['house', 'cuddy', 'chase', 'thirteen', wilson], the list comprehension [doc[0] for doc in doctor] produces the list ['h', 'c', 'c', 't', 'w'].

Nested List Comprehension

matrix = [[col for col in range(5)] for row in range(5)]

#[[0, 1, 2, 3, 4],[0, 1, 2, 3, 4],[0, 1, 2, 3, 4],[0, 1, 2, 3, 4],[0, 1, 2, 3, 4]]

#也可以只打印单独每一行
for row in matrix:
    print(row)          

To create the list of lists, you simply have to supply the list comprehension as the output expression of the overall list comprehension:

[[output expression] for iterator variable in iterable]

Conditionals in comprehensions

new_nums = [num + 1 for num in nums]