变量不会从主函数传递到其他函数答案

【问题标题】：Variables don't pass from main function to other functions变量不会从主函数传递到其他函数
【发布时间】：2020-12-15 11:27:11
【问题描述】：

我正在尝试构建一个网络爬虫。我制作了一个返回 cookie 和标头的函数。为简单起见，我的代码示例是一个常量值，我只设置标头，但通常它会通过请求获取值。另一个函数从网站获取图像链接，但为此它需要标题。我在我的主函数上定义了标题，然后我调用了 get_photos 函数，但它说标题没有定义。

import requests
from bs4 import BeautifulSoup as bs
s = requests.session()

def login():
    headers = {'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:83.0) Gecko/20100101 Firefox/83.0'}
    return headers

def get_photos():
    response = requests.get('https://upload.wikimedia.org/wikipedia/en/thumb/a/a9/Example.jpg/111px-Example.jpg', headers=headers)
    return response

def main():
    """That's where the magic happens."""
    headers = login()
    print(get_photos())

if __name__ == "__main__":
    main()

我得到的错误是：

Traceback (most recent call last):
  File "/home/archie/evip/example.py", line 19, in <module>
    main()
  File "/home/archie/evip/example.py", line 16, in main
    print(get_photos())
  File "/home/archie/evip/example.py", line 9, in get_photos
    response = requests.get('https://upload.wikimedia.org/wikipedia/en/thumb/a/a9/Example.jpg/111px-Example.jpg', headers=headers)
NameError: name 'headers' is not defined

【问题讨论】：

当然，get_photos 范围内的任何地方都没有 headers。最简单的方法是将headers 作为参数传递给get_photos

标签： python function oop beautifulsoup

【解决方案1】：

您需要将 headers 变量传递给get_photos(headers)。

import requests
from bs4 import BeautifulSoup as bs
s = requests.session()

def login():
    headers = {'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:83.0) Gecko/20100101 Firefox/83.0'}
    return headers

def get_photos(headers):
    response = requests.get('https://upload.wikimedia.org/wikipedia/en/thumb/a/a9/Example.jpg/111px-Example.jpg', headers=headers)
    return response

def main():
    """That's where the magic happens."""
    print(get_photos(login()))

if __name__ == "__main__":
    main()

【讨论】：

【解决方案2】：

您可以修改您的代码以使 headers 在 get_photos 方法的范围内

import requests
from bs4 import BeautifulSoup as bs
s = requests.session()

def login():
    headers = {'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64; rv:83.0) Gecko/20100101 Firefox/83.0'}
    return headers

def get_photos(headers):
    response = requests.get('https://upload.wikimedia.org/wikipedia/en/thumb/a/a9/Example.jpg/111px-Example.jpg', headers=headers)
    return response

def main():
    """That's where the magic happens."""
    headers = login()
    print(get_photos(headers))

if __name__ == "__main__":
    main()

检查main中的get_photos方法调用。

这是由于scope of variables.

【讨论】：