尝试在任何地方定义全局变量时，我得到“无效语法”

Question

我目前正在尝试制作一个刽子手游戏。我已经在任何函数之外定义了变量“lives”，但是当尝试在 start_game 函数中使用它时，编辑器说该变量已定义但从未使用过。但是，当我尝试将它声明为全局时，无论它是在函数内部还是外部，它都会给我一个“无效语法”错误——特别是在赋值运算符“=”处。

import random

words = "dog cat log hog etc"     # <-- just a huge string of a bunch of words

words = words.split()

word = random.choice(words)

# Difficulties: Easy:12 Medium:9 Hard:6

lives = 0

current = "_" * len(word)

def gameLoop():

  while current != word and lives > 0:

    print("Guess a letter. If you wish to exit the game, enter 'exit'")

    input("")

    print(lives)

def start_game():

  while True:

    print("Welcome to Hangman! What game mode would you like to play? Easy, medium, or hard?")

    game_mode = str.lower(input(""))

   if game_mode == "easy":

      lives = 12

      gameLoop()

      break

    elif game_mode == "medium":

      lives = 9

      gameLoop()

      break

    elif game_mode == "hard":

      lives = 6

      gameLoop()

      break

start_game()

Answer 1

在我写这个问题的时候，我意识到我做错了什么，所以我决定继续自己回答这个问题。当您将变量定义为全局变量时，您不想像这样为变量分配一个变量：global&nbsp;lives&nbsp;=&nbsp;0那会给你一个错误。为什么？当你想将一个变量定义为全局变量时，你是在告诉计算机，“嘿，这里的这个变量是全局使用的，而不是本地使用的。”&nbsp;上面这行代码的问题在于，您还为变量分配了一个值，而此时您应该做的就是告诉计算机该变量是全局的。如果你想给变量赋值（无论是第一次还是重新赋值），那么你需要在不同的代码行上赋值。当我查找这个时，我没有发现任何明确的说法，所以我希望这有助于任何使用 python 编码的新人或者像我一样忘记它是如何工作的人。

Answer 2

首先，global语句是声明，而不是可执行语句。它只是告诉解释器查看模块命名空间而不是函数调用命名空间。它只需要在函数内部使用。在外面，本地和全局命名空间是同一个东西（模块命名空间），所以该global语句什么都不做。该语句必须是关键字，global后跟要被视为全局名称的逗号分隔列表。如果要为任何名称赋值，无论是否为全局名称，都必须在单独的赋值语句中进行。您可能想要更像下面的代码的东西，它会按照您的需要“工作”（我意识到这只是开发中的部分程序）。我修复了缩进以符合 PEP 8，因为我的老眼睛发现否则很难阅读代码！import randomwords = "tom dick harry".split()word = random.choice(words)# Difficulties: Easy:12 Medium:9 Hard:6lives = 0current = "_" * len(word)def gameLoop():&nbsp; &nbsp; global lives&nbsp; &nbsp; while current != word and lives > 0:&nbsp; &nbsp; &nbsp; &nbsp; print("Guess a letter. If you wish to exit the game, enter 'exit'")&nbsp; &nbsp; &nbsp; &nbsp; input("")&nbsp; &nbsp; &nbsp; &nbsp; print(lives)def start_game():&nbsp; &nbsp; global lives&nbsp; &nbsp; while True:&nbsp; &nbsp; &nbsp; &nbsp; print(&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; "Welcome to Hangman! What game mode would you like to play? Easy, medium, or hard?"&nbsp; &nbsp; &nbsp; &nbsp; )&nbsp; &nbsp; &nbsp; &nbsp; game_mode = str.lower(input(""))&nbsp; &nbsp; &nbsp; &nbsp; if game_mode == "easy":&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; lives = 12&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; gameLoop()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break&nbsp; &nbsp; &nbsp; &nbsp; elif game_mode == "medium":&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; lives = 9&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; gameLoop()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break&nbsp; &nbsp; &nbsp; &nbsp; elif game_mode == "hard":&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; lives = 6&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; gameLoop()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; breakstart_game()