Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python3
import sys, math, fractions, itertools

YES = "Yes"  # type: str
NO = "No"  # type: str

def solve(H: int, W: int, s: "List[str]"):
    flag = True
    for h in range(H):
        for w in range(W):
            if s[h][w] == '#':
                if h == H-1: U = True
                else: U = s[h+1][w] != '#'
                if h == 0: D = True
                else: D = s[h-1][w] != '#'
                if w == 0: L = True
                else: L = s[h][w-1] != '#'
                if w == W-1: R = True
                else: R = s[h][w+1] != '#'
                if all([U, D, L, R]):
                    flag = False
    if flag:
        print('Yes')
    else:
        print('No')
    return


# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    W = int(next(tokens))  # type: int
    s = [ next(tokens) for _ in range(W) ]  # type: "List[str]"
    solve(H, W, s)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys, math, fractions, itertools

YES = "Yes"  # type: str
NO = "No"  # type: str

def solve(H: int, W: int, s: "List[str]"):
    flag = True
    for h in range(H):
        for w in range(W):
            if s[h][w] == '#':
                if h == H-1: U = True
                else: U = s[h+1][w] != '#'
                if h == 0: D = True
                else: D = s[h-1][w] != '#'
                if w == 0: L = True
                else: L = s[h][w-1] != '#'
                if w == W-1: R = True
                else: R = s[h][w+1] != '#'
                if all([U, D, L, R]):
                    flag = False
    if flag:
        print('Yes')
    else:
        print('No')
    return


# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    W = int(next(tokens))  # type: int
    s = [ next(tokens) for _ in range(H) ]  # type: "List[str]"
    solve(H, W, s)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python3
import sys, math, fractions, itertools

YES = "Yes"  # type: str
NO = "No"  # type: str

def solve(H: int, W: int, s: "List[str]"):
    flag = True
    for h in range(H):
        for w in range(W):
            if s[h][w] == '#':
                if h == H-1: U = False
                else: U = s[h+1][w] != '#'
                if h == 0: D = False
                else: D = s[h-1][w] != '#'
                if w == 0: L = False
                else: L = s[h][w-1] != '#'
                if w == W-1: R = False
                else: R = s[h][w+1] != '#'
                if all([U, D, L, R]):
                    flag = False
    if flag:
        print('Yes')
    else:
        print('No')
    return


# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    W = int(next(tokens))  # type: int
    s = [ next(tokens) for _ in range(W) ]  # type: "List[str]"
    solve(H, W, s)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys, math, fractions, itertools

YES = "Yes"  # type: str
NO = "No"  # type: str

def solve(H: int, W: int, s: "List[str]"):
    flag = True
    for h in range(H):
        for w in range(W):
            if s[h][w] == '#':
                if h == H-1: U = True
                else: U = s[h+1][w] != '#'
                if h == 0: D = True
                else: D = s[h-1][w] != '#'
                if w == 0: L = True
                else: L = s[h][w-1] != '#'
                if w == W-1: R = True
                else: R = s[h][w+1] != '#'
                if all([U, D, L, R]):
                    flag = False
    if flag:
        print('Yes')
    else:
        print('No')
    return


# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    W = int(next(tokens))  # type: int
    s = [ next(tokens) for _ in range(H) ]  # type: "List[str]"
    solve(H, W, s)

if __name__ == '__main__':
    main()