## List Comprehensions
matrix = [[1, 2, 3], [4, 5, 6]]

# for loop
negative_matrix = []
for row in matrix:
    negative_matrix.append([-n for n in row])

# list comprehension
negative_evens_matrix = [
    [-n for n in row] for row in matrix if n % 2 == 0  # or negate(n)
]

from itertools import izip

list(zip(*matrix))  # returns tuples
print([list(col) for col in izip(*matrix)])
