Buggy python submission (verdict: Runtime Error):
while 1:
        H,W = map(int, raw_input().split())
        if H == W == 0:
                break
        for i in range(H):
                if i % 2 == 0:
                        if W % 2 == 0:
                                print "#." * (W / 2)
                        else:
                                print no                                         
                else:
                        if W % 2 == 0:
                                print ".#" * (W / 2)
                        else:
                                print no

Fixed submission:
while 1:
        H,W = map(int, raw_input().split())
        if H + W == 0:
                break
        for i in range(H):
                if i % 2 == 0:
                        if W % 2 == 0:
                                print "#." * (W / 2)
                        else:
                                print "#." * (W / 2) + "#"                       
                else:
                        if W % 2 == 0:
                                print ".#" * (W / 2)
                        else:
                                print ".#" * (W / 2) +"."
        print ""

Buggy python submission (verdict: Runtime Error):
while 1:
        H,W = map(int, raw_input()
        if H == W == 0:
                break
        for i in range(H):
                if i % 2 == 0:
                        if W % 2 == 0:
                                print "#." * (W / 2)
                        else:
                                print "#." * (W / 2) + "#"                       
                else:
                        if W % 2 == 0:
                                print ".#" * (W / 2)
                        else:
                                print ".#" * (W / 2) +"."

Fixed submission:
while 1:
        H,W = map(int, raw_input().split())
        if H + W == 0:
                break
        for i in range(H):
                if i % 2 == 0:
                        if W % 2 == 0:
                                print "#." * (W / 2)
                        else:
                                print "#." * (W / 2) + "#"                       
                else:
                        if W % 2 == 0:
                                print ".#" * (W / 2)
                        else:
                                print ".#" * (W / 2) +"."
        print ""

Buggy python submission (verdict: Runtime Error):
while 1:
        H,W = map(int, raw_input().split())
        if H + W == 0:
                break
        for i in range(H):
                if i % 2 == 0:
                        if W % 2 == 0:
                                print "#." * (W / 2)
                        else:
                                print "#." * (W / 2) + "#"                       
                else:
                        if W % 2 == 0:
                                print ".#" * (W / 2)
                        else:
                                print ".#" * (W / 2) +"."
         print ""

Fixed submission:
while 1:
        H,W = map(int, raw_input().split())
        if H + W == 0:
                break
        for i in range(H):
                if i % 2 == 0:
                        if W % 2 == 0:
                                print "#." * (W / 2)
                        else:
                                print "#." * (W / 2) + "#"                       
                else:
                        if W % 2 == 0:
                                print ".#" * (W / 2)
                        else:
                                print ".#" * (W / 2) +"."
        print ""