n-Queens Problem

nQueen.py

BOARD_SIZE = 4

def under_attack(col, queens): 
    left = right = col
    for r, c in reversed(queens): 
        left, right = left-1, right+1
        if c in (left, col, right):
            return True
    return False

def solve(n):
    if n == 0: return [[]]
    smaller_solutions = solve(n-1) 
    return [solution+[(n,i+1)] 
        for i in range(BOARD_SIZE)
            for solution in smaller_solutions
                if not under_attack(i+1, solution)]
                
for answer in solve(BOARD_SIZE): print answer