全局变量在函数之外不起作用

Question

我需要你的帮助。为什么会出现此错误？title被指定为全局变量，所以我应该打印出"None"，对吗？

def get_history_events(requests, BeautifulSoup):
global title, facts
title = facts = None
url = 'https://cs.wikipedia.org/wiki/Hlavn%C3%AD_strana'
header = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0'}
r = requests.get(url, headers=header).text
soup = BeautifulSoup(r, 'lxml')
table = soup.find('div', class_ = 'mainpage-block calendar-container')
title = table.find('div', class_ = 'mainpage-headline').text
facts = table.find('ul').text
print(title)
# NameError: name 'title' is not defined

Answer 1

您需要首先在全局作用域中声明变量

例如：

title = None
def get_history_events(requests, BeautifulSoup):
global title, facts
title = facts = None
url = 'https://cs.wikipedia.org/wiki/Hlavn%C3%AD_strana'
header = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0'}
r = requests.get(url, headers=header).text
soup = BeautifulSoup(r, 'lxml')
table = soup.find('div', class_ = 'mainpage-block calendar-container')
title = table.find('div', class_ = 'mainpage-headline').text
facts = table.find('ul').text
print(title)

或者在调用print之前执行您的函数：例如：

def get_history_events(requests, BeautifulSoup):
global title, facts
title = facts = None
url = 'https://cs.wikipedia.org/wiki/Hlavn%C3%AD_strana'
header = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0'}
r = requests.get(url, headers=header).text
soup = BeautifulSoup(r, 'lxml')
table = soup.find('div', class_ = 'mainpage-block calendar-container')
title = table.find('div', class_ = 'mainpage-headline').text
facts = table.find('ul').text
get_history_events(<imagine your args here>)
print(title)

Answer 2

您还没有运行您的函数，所以运行代码从来没有看到过您的全局语句。

要使代码工作，请首先调用您的函数：

get_history_events(...)
print(title)

以下是一组可供全球使用的优秀示例：https://www.programiz.com/python-programming/global-keyword

Answer 3

感谢大家。固定的工作正常。