Buggy python submission (verdict: Time Limit Exceeded):
import sys
import collections


def solve():
    readline = sys.stdin.buffer.readline
    mod = 10 ** 9 + 7
    h, w = list(map(int, readline().split()))
    a = [list(str(readline().rstrip().decode('utf-8'))) for _ in range(h)]

    ql = [[0, 0, 0]]
    ql = collections.deque(ql)
    cl = collections.defaultdict(int)
    cl[0, 0] = 1
    while True:
        if len(ql) != 0:
            cost, x, y = ql.popleft()
            for xv, yv in [[x + 1, y], [x, y + 1]]:
                if 0 <= xv < h and 0 <= yv < w:
                    if a[xv][yv] != "#":
                        ql.append([cost + 1, xv, yv])
                        cl[xv, yv] = cl[x, y]
                        a[xv][yv] = "#"
                    else:
                        cl[xv, yv] += cl[x, y]
                        cl[xv, yv] % mod
        else:
            break
    print(cl[h-1, w-1] % mod)


if __name__ == '__main__':
    solve()


Fixed submission:
import sys


def solve():
    input = sys.stdin.readline
    mod = 10 ** 9 + 7
    h, w = list(map(int, input().rstrip('\n').split()))
    a = [list(str(input().rstrip('\n'))) for _ in range(h)]
    dp = [[0] * w for _ in range(h)]
    for i in range(h):
        for j in range(w):
            if a[i][j] == "#":
                dp[i][j] = 0
            elif i == 0 and j == 0:
                dp[i][j] = 1
            elif i == 0:
                dp[i][j] = dp[i][j-1]
            elif j == 0:
                dp[i][j] = dp[i-1][j]
            else:
                dp[i][j] = (dp[i-1][j] + dp[i][j-1]) % mod
    print(dp[-1][-1])


if __name__ == '__main__':
    solve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import collections


def solve():
    readline = sys.stdin.buffer.readline
    mod = 10 ** 9 + 7
    h, w = list(map(int, readline().split()))
    a = [list(str(readline().rstrip().decode('utf-8'))) for _ in range(h)]

    ql = [[0, 0, 0]]
    ql = collections.deque(ql)
    fq = collections.defaultdict(list)
    fq[0, 0]
    cl = collections.defaultdict(int)
    cl[0, 0] = 1
    while True:
        if len(ql) != 0:
            cost, x, y = ql.popleft()
            for xv, yv in [[x + 1, y], [x, y + 1]]:
                if 0 <= xv < h and 0 <= yv < w:
                    if (xv, yv) not in fq and a[xv][yv] != "#":
                        ql.append([cost + 1, xv, yv])
                        fq[xv, yv] = cost + 1
                        cl[xv, yv] = cl[x, y]
                    else:
                        cl[xv, yv] += cl[x, y]
                        cl[xv, yv] % mod
        else:
            break
    print(cl[h-1, w-1] % mod)


if __name__ == '__main__':
    solve()


Fixed submission:
import sys


def solve():
    input = sys.stdin.readline
    mod = 10 ** 9 + 7
    h, w = list(map(int, input().rstrip('\n').split()))
    a = [list(str(input().rstrip('\n'))) for _ in range(h)]
    dp = [[0] * w for _ in range(h)]
    for i in range(h):
        for j in range(w):
            if a[i][j] == "#":
                dp[i][j] = 0
            elif i == 0 and j == 0:
                dp[i][j] = 1
            elif i == 0:
                dp[i][j] = dp[i][j-1]
            elif j == 0:
                dp[i][j] = dp[i-1][j]
            else:
                dp[i][j] = (dp[i-1][j] + dp[i][j-1]) % mod
    print(dp[-1][-1])


if __name__ == '__main__':
    solve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import collections


def solve():
    input = sys.stdin.readline
    mod = 10 ** 9 + 7
    h, w = list(map(int, input().rstrip('\n').split()))
    a = [list(str(input().rstrip('\n'))) for _ in range(h)]

    ql = [[0, 0, 0]]
    ql = collections.deque(ql)
    fq = collections.defaultdict(int)
    fq[0, 0] = 1
    while True:
        if len(ql) != 0:
            cost, xv, yv = ql.popleft()
            for xvv, yvv in [[xv + 1, yv], [xv, yv + 1]]:
                if 0 <= xvv < h and 0 <= yvv < w:
                    if (xvv, yvv) not in fq and a[xvv][yvv] != "#":
                        ql.append([cost + 1, xvv, yvv])
                        fq[xvv, yvv] = fq[xv, yv]
                    else:
                        fq[xvv, yvv] += fq[xv, yv]
        else:
            break
    print(fq[h-1, w-1] % mod)


if __name__ == '__main__':
    solve()


Fixed submission:
import sys


def solve():
    input = sys.stdin.readline
    mod = 10 ** 9 + 7
    h, w = list(map(int, input().rstrip('\n').split()))
    a = [list(str(input().rstrip('\n'))) for _ in range(h)]
    dp = [[0] * w for _ in range(h)]
    for i in range(h):
        for j in range(w):
            if a[i][j] == "#":
                dp[i][j] = 0
            elif i == 0 and j == 0:
                dp[i][j] = 1
            elif i == 0:
                dp[i][j] = dp[i][j-1]
            elif j == 0:
                dp[i][j] = dp[i-1][j]
            else:
                dp[i][j] = (dp[i-1][j] + dp[i][j-1]) % mod
    print(dp[-1][-1])


if __name__ == '__main__':
    solve()