Łukasz Langa.py

# This code is horrible but you wanted the computation to be done in a single
# generator expression. Cheers!

import json
import sys

def resize(grid):
    for line in grid:
        line.extend(['.'] * 3)
    header = [['.'] * 10] * 3
    grid.extend(header)
    header.extend(grid)
    return header

def search(file):
    grid = json.load(file)
    line_count = len(grid)
    line_length = len(grid[0])
    grid = resize(grid)

    for result in (set(grid[i+m][j+n] for m, n in zip(iter1, iter2))
        for iter1, iter2 in (([0] * 4, range(4)), (range(4), [0] * 4),
            (range(4), range(4)), (range(0, -4, -1), range(4)))
            for i in range(3, line_count+3) for j in range(line_length)):
        if result == {'O'}:
            return 'Winner: O'
        elif result == {'X'}:
            return 'Winner: X'
    return 'No winner'

if __name__ == '__main__':
    print(search(sys.stdin))