Snake moves

#!/usr/local/bin/python3.7
# -*- coding: utf-8 -*import
from _collections import deque

rows, columns = map(int, input().split())

snake_string = input()

matrix = [[None] * columns for _ in range(rows)]

snake = deque(snake_string)

for x in range(rows):
    if x % 2 == 0:
        for y in range(columns):
            if not snake:
                snake = deque(snake_string)
            matrix[x][y] = snake.popleft()
    else:
        for y in range(columns -1, -1, -1):
            if not snake:
                snake = deque(snake_string)
            matrix[x][y] = snake.popleft()

print('\n'.join([''.join([y for y in x]) for x in matrix]))