Transpose a matrix in Python

transpose.py

def transpose(matrix):
    num_rows = len(matrix)
    num_cols = len(matrix[0])
    t_matrix = [[None for _ in range(num_rows)] for _ in range(num_cols)]
    for y in range(num_rows):
        for x in range(num_cols):
            t_matrix[x][y] = matrix[y][x]
    return t_matrix