list comprehension python
# All of the possibilies that can be done with the List Comprehension vec = [-4, -2, 0, 2, 4] # create a new list with the values doubled doubled = [x*2 for x in vec] # [-8, -4, 0, 4, 8] # filter the list to exclude negative numbers greater_thatn_0 = [x for x in vec if x >= 0] # output [0, 2, 4] # apply a function to all the elements positive = [abs(x) for x in vec] # output [4, 2, 0, 2, 4] # call a method on each element freshfruit = [' banana', ' loganberry ', 'passion fruit '] fruits_nospaces = [weapon.strip() for weapon in freshfruit] # output ['banana', 'loganberry', 'passion fruit'] # create a list of 2-tuples like (number, square) squares = [(x, x**2) for x in range(6)] # output [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)] # the tuple must be parenthesized, otherwise an error is raised # error = [x, x**2 for x in range(6)] # error = [x, x**2 for x in range(6)] ^ # SyntaxError: invalid syntax # flatten a list using a listcomp with two 'for' vec = [[1,2,3], [4,5,6], [7,8,9]] unpacking_tuple = [num for elem in vec for num in elem] # output [1, 2, 3, 4, 5, 6, 7, 8, 9]
