Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(10**7)

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    # 上下左右の配列
    r_arr = [[0 for w in range(W)] for h in range(H)]
    l_arr = [[0 for w in range(W)] for h in range(H)]
    u_arr = [[0 for w in range(W)] for h in range(H)]
    d_arr = [[0 for w in range(W)] for h in range(H)]

    # 左から
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 1:
                continue
            else:
                if w == 0:
                    val = 1
                else:
                    val = l_arr[h][w-1] + 1
            l_arr[h][w] = val

    # 上から
    for w in range(W):
        for h in range(H):
            if s_arr[h][w] == 1:
                continue
            else:
                if h == 0:
                    val = 1
                else:
                    val = u_arr[h-1][w] + 1
            u_arr[h][w] = val

    # 右から
    for h in range(H):
        for w in reversed(range(W)):
            if s_arr[h][w] == 1:
                continue
            else:
                if w == W-1:
                    val = 1
                else:
                    val = r_arr[h][w+1] + 1
            r_arr[h][w] = val

    # 下から
    for w in range(W):
        for h in reversed(range(H)):
            if s_arr[h][w] == 1:
                continue
            else:
                if h == H-1:
                    val = 1
                else:
                    val = d_arr[h + 1][w] + 1
            d_arr[h][w] = val

    mx_ans = 0
    for h in range(H):
        for w in range(W):
            ans = l_arr[h][w] + r_arr[h][w] + u_arr[h][w] + d_arr[h][w] - 3
            if ans >= mx_ans:
                mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    h_count = [[-1 for w in range(W)] for h in range(H)]
    w_count = [[-1 for w in range(W)] for h in range(H)]

    # w_countを埋める
    for h in range(H):
        row = s_arr[h]
        clearFlag = True
        for w, s in enumerate(row):
            if clearFlag:
                start = w
                end = w
            if s == 0:
                end = w
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for iw in range(start, end+1):
                        w_count[h][iw] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for iw in range(start, max(end + 1, W)):
                w_count[h][iw] = end - start + 1

    # h_countを埋める
    for w in range(W):
        col = [row[w] for row in s_arr]
        clearFlag = True
        for h, s in enumerate(col):
            if clearFlag:
                start = h
                end = h
            if s == 0:
                end = h
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for ih in range(start, end+1):
                        h_count[ih][w] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for ih in range(start, max(end+1, H)):
                h_count[ih][w] = end - start + 1

    dmatprint(h_count)
    dmatprint(w_count)
    mx_ans = 0
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 0:
                ans = h_count[h][w] + w_count[h][w] - 1
                if ans >= mx_ans:
                    mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(10**7)
import numpy as np

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    h_count = [[-1 for w in range(W)] for h in range(H)]
    w_count = [[-1 for w in range(W)] for h in range(H)]

    # w_countを埋める
    for h in range(H):
        row = s_arr[h]
        clearFlag = True
        for w, s in enumerate(row):
            if clearFlag:
                start = w
                end = w
            if s == 0:
                end = w
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for iw in range(start, end+1):
                        w_count[h][iw] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for iw in range(start, max(end + 1, W)):
                w_count[h][iw] = end - start + 1

    # h_countを埋める
    for w in range(W):
        col = [row[w] for row in s_arr]
        clearFlag = True
        for h, s in enumerate(col):
            if clearFlag:
                start = h
                end = h
            if s == 0:
                end = h
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for ih in range(start, end+1):
                        h_count[ih][w] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for ih in range(start, max(end+1, H)):
                h_count[ih][w] = end - start + 1

    dmatprint(h_count)
    dmatprint(w_count)
    mx_ans = 0
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 0:
                ans = h_count[h][w] + w_count[h][w] - 1
                if ans >= mx_ans:
                    mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    h_count = [[-1 for w in range(W)] for h in range(H)]
    w_count = [[-1 for w in range(W)] for h in range(H)]

    # w_countを埋める
    for h in range(H):
        row = s_arr[h]
        clearFlag = True
        for w, s in enumerate(row):
            if clearFlag:
                start = w
                end = w
            if s == 0:
                end = w
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for iw in range(start, end+1):
                        w_count[h][iw] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for iw in range(start, max(end + 1, W)):
                w_count[h][iw] = end - start + 1

    # h_countを埋める
    for w in range(W):
        col = [row[w] for row in s_arr]
        clearFlag = True
        for h, s in enumerate(col):
            if clearFlag:
                start = h
                end = h
            if s == 0:
                end = h
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for ih in range(start, end+1):
                        h_count[ih][w] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for ih in range(start, max(end+1, H)):
                h_count[ih][w] = end - start + 1

    dmatprint(h_count)
    dmatprint(w_count)
    mx_ans = 0
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 0:
                ans = h_count[h][w] + w_count[h][w] - 1
                if ans >= mx_ans:
                    mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()

Buggy python submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10**7)
import numpy as np

#debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)

def solve():
    H, W = map(int, input().split())
    s_arr = np.zeros(shape=(H, W))
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h, w] = 0
            else:
                s_arr[h, w] = 1

    memo = [[(-1, -1) for w in range(W)] for h in range(H)]

    def count_light(arr, pos):
        start = 0
        end = 0
        active = False
        for i, s in enumerate(arr):
            if i == pos:
                active = True
            if s == 1:
                if active == True:
                    return (start, end)
                else:
                    start = i + 1
                    end = i + 1
            else:
                end = i
        return start, end

    def count_hw_light(h, w):
        if s_arr[h][w] == 1:
            return 0

        m = memo[h][w] # (3, 2) / (-1, -1) / ( -1, 2) / (3, -1)
        dprint(h, w, m)
        count = 0
        counth = m[0]
        countw = m[1]
        if counth == -1:
            arr = s_arr[:, w]
            start, end = count_light(arr, h)
            count += (end - start) + 1
            dprint("h", arr, h, end, start)
            for i in range(start, end+1):
                memo[i][w] = ((end - start) + 1, countw)
        else:
            count += counth

        if countw == -1:
            arr = s_arr[h, :]
            start, end = count_light(arr, w)
            count += (end - start) + 1
            dprint("w", arr, w, end, start)
            for i in range(start, end+1):
                memo[h][i] = (counth, (end - start) + 1)
        else:
            count += countw

        dprint(h, w, memo[h][w], counth, countw, count)
        dprint(memo)
        return count

    mx_ans = 0
    for h in range(H):
        for w in range(W):
            ans = count_hw_light(h, w) -1 # 重複カウント消し
            if ans >= mx_ans:
                mx_ans = ans

    print(mx_ans)
    dprint(s_arr)
    dprint(memo)

solve()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    h_count = [[-1 for w in range(W)] for h in range(H)]
    w_count = [[-1 for w in range(W)] for h in range(H)]

    # w_countを埋める
    for h in range(H):
        row = s_arr[h]
        clearFlag = True
        for w, s in enumerate(row):
            if clearFlag:
                start = w
                end = w
            if s == 0:
                end = w
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for iw in range(start, end+1):
                        w_count[h][iw] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for iw in range(start, max(end + 1, W)):
                w_count[h][iw] = end - start + 1

    # h_countを埋める
    for w in range(W):
        col = [row[w] for row in s_arr]
        clearFlag = True
        for h, s in enumerate(col):
            if clearFlag:
                start = h
                end = h
            if s == 0:
                end = h
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for ih in range(start, end+1):
                        h_count[ih][w] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for ih in range(start, max(end+1, H)):
                h_count[ih][w] = end - start + 1

    dmatprint(h_count)
    dmatprint(w_count)
    mx_ans = 0
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 0:
                ans = h_count[h][w] + w_count[h][w] - 1
                if ans >= mx_ans:
                    mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(10**7)
import numpy as np


def solve():
    H, W = map(int, input().split())
    s_arr = np.zeros(shape=(H, W))
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h, w] = 0
            else:
                s_arr[h, w] = 1

    memo = [[(-1, -1) for w in range(W)] for h in range(H)]

    def count_light(arr, pos):
        start = 0
        end = 0
        active = False
        for i, s in enumerate(arr):
            if i == pos:
                active = True
            if s == 1:
                if active == True:
                    return (start, end)
                else:
                    start = i + 1
                    end = i + 1
            else:
                end = i
        return start, end

    def count_hw_light(h, w):
        if s_arr[h][w] == 1:
            return 0

        m = memo[h][w] # (3, 2) / (-1, -1) / ( -1, 2) / (3, -1)
        count = 0
        counth = m[0]
        countw = m[1]
        if counth == -1:
            arr = s_arr[:, w]
            start, end = count_light(arr, h)
            count += (end - start) + 1
            for i in range(start, end+1):
                memo[i][w] = ((end - start) + 1, countw)
        else:
            count += counth

        if countw == -1:
            arr = s_arr[h, :]
            start, end = count_light(arr, w)
            count += (end - start) + 1
            for i in range(start, end+1):
                memo[h][i] = (counth, (end - start) + 1)
        else:
            count += countw

        return count

    mx_ans = 0
    for h in range(H):
        for w in range(W):
            ans = count_hw_light(h, w) -1 # 重複カウント消し
            if ans >= mx_ans:
                mx_ans = ans

    print(mx_ans)

solve()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    h_count = [[-1 for w in range(W)] for h in range(H)]
    w_count = [[-1 for w in range(W)] for h in range(H)]

    # w_countを埋める
    for h in range(H):
        row = s_arr[h]
        clearFlag = True
        for w, s in enumerate(row):
            if clearFlag:
                start = w
                end = w
            if s == 0:
                end = w
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for iw in range(start, end+1):
                        w_count[h][iw] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for iw in range(start, max(end + 1, W)):
                w_count[h][iw] = end - start + 1

    # h_countを埋める
    for w in range(W):
        col = [row[w] for row in s_arr]
        clearFlag = True
        for h, s in enumerate(col):
            if clearFlag:
                start = h
                end = h
            if s == 0:
                end = h
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for ih in range(start, end+1):
                        h_count[ih][w] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for ih in range(start, max(end+1, H)):
                h_count[ih][w] = end - start + 1

    dmatprint(h_count)
    dmatprint(w_count)
    mx_ans = 0
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 0:
                ans = h_count[h][w] + w_count[h][w] - 1
                if ans >= mx_ans:
                    mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(10**7)
import numpy as np

#debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)

def solve():
    H, W = map(int, input().split())
    s_arr = np.zeros(shape=(H, W))
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h, w] = 0
            else:
                s_arr[h, w] = 1

    memo = [[(-1, -1) for w in range(W)] for h in range(H)]

    def count_light(arr, pos):
        start = 0
        end = 0
        active = False
        for i, s in enumerate(arr):
            if i == pos:
                active = True
            if s == 1:
                if active == True:
                    return (start, end)
                else:
                    start = i + 1
                    end = i + 1
            else:
                end = i
        return start, end

    def count_hw_light(h, w):
        if s_arr[h][w] == 1:
            return 0

        m = memo[h][w] # (3, 2) / (-1, -1) / ( -1, 2) / (3, -1)
        dprint(h, w, m)
        count = 0
        counth = m[0]
        countw = m[1]
        if counth == -1:
            arr = s_arr[:, w]
            start, end = count_light(arr, h)
            count += (end - start) + 1
            dprint("h", arr, h, end, start)
            for i in range(start, end+1):
                memo[i][w] = ((end - start) + 1, countw)
        else:
            count += counth

        if countw == -1:
            arr = s_arr[h, :]
            start, end = count_light(arr, w)
            count += (end - start) + 1
            dprint("w", arr, w, end, start)
            for i in range(start, end+1):
                memo[h][i] = (counth, (end - start) + 1)
        else:
            count += countw

        dprint(h, w, memo[h][w], counth, countw, count)
        dprint(memo)
        return count

    mx_ans = 0
    for h in range(H):
        for w in range(W):
            ans = count_hw_light(h, w) -1 # 重複カウント消し
            if ans >= mx_ans:
                mx_ans = ans

    print(mx_ans)

    dprint(s_arr)
    dprint(memo)

solve()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)

debug = True
debug = False

def dprint(*objects):
    if debug == True:
        print(*objects)
def dmatprint(mat):

    if debug == True:
        for row in mat:
            for col in row:
                print("{0:2d} ".format(col), end="")
            print("")
        print("")

def solve():
    H, W = map(int, input().split())
    s_arr = [[-1 for w in range(W)] for h in range(H)]
    for h in range(H):
        s_row = input()
        for w in range(W):
            if s_row[w] == ".":
                s_arr[h][w] = 0
            else:
                s_arr[h][w] = 1

    h_count = [[-1 for w in range(W)] for h in range(H)]
    w_count = [[-1 for w in range(W)] for h in range(H)]

    # w_countを埋める
    for h in range(H):
        row = s_arr[h]
        clearFlag = True
        for w, s in enumerate(row):
            if clearFlag:
                start = w
                end = w
            if s == 0:
                end = w
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for iw in range(start, end+1):
                        w_count[h][iw] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for iw in range(start, max(end + 1, W)):
                w_count[h][iw] = end - start + 1

    # h_countを埋める
    for w in range(W):
        col = [row[w] for row in s_arr]
        clearFlag = True
        for h, s in enumerate(col):
            if clearFlag:
                start = h
                end = h
            if s == 0:
                end = h
                clearFlag = False
            else:
                if clearFlag:
                    h_count[h][w] = -1
                else:
                    for ih in range(start, end+1):
                        h_count[ih][w] = end - start + 1
                clearFlag = True
        if clearFlag == False:
            for ih in range(start, max(end+1, H)):
                h_count[ih][w] = end - start + 1

    dmatprint(h_count)
    dmatprint(w_count)
    mx_ans = 0
    for h in range(H):
        for w in range(W):
            if s_arr[h][w] == 0:
                ans = h_count[h][w] + w_count[h][w] - 1
                if ans >= mx_ans:
                    mx_ans = ans

    print(mx_ans)
    dmatprint(s_arr)
solve()