在函数中创建python 3中的全局变量 [英] Creating global variable in python 3 from functions

问题描述

我想知道为什么我不能在函数结束后访问变量：variable_for_raw_data。代码如下：

  def htmlfrom（Website_URL）：
导入urllib.request 
 response = urllib.request.urlopen（Website_URL）
 variable_for_raw_data =（input（这个数据将被保存为：））
全局变量_for_raw_data 
 variable_for_raw_data = response.read（）
  

现在为什么我不能在函数结束后访问变量variable_for_raw_data？

注意事项：

Python 3.3
urllib NOT urllib2

解决方案

它看起来像你试图动态创建变量，我想你的代码看起来像这样。

  def htmlfrom（website_url）：
 import urllib.request 
 response = urllib.request.urlopen（website_url）
 variable_for_raw_data =（input（这个数据是什么保存为：））
全局variable_for_raw_data 
 variable_for_raw_data = r esponse.read（）
 
 
 if __name__ ==__main__：
 
 htmlfrom（www.stackoverflow.com）
 
 #html_stackoverflow永远不会被创建它的值是
 #of variable_for_raw_data before variable_for_raw_data 
＃被response.read（）重写
 
＃输入信息不会创建一个变量
 print（html_stackoverflow）
  

以下是我要做的事情：

 导入urllib.request 
 
 def htmlfrom（website_url）：
'''
 docstrings 
'''
 
 response = urllib.request.urlopen（website_url）
 variable_for_raw_data = response.read（）
 return variable_for_raw_data 
 
 if __name__ ==__main__：
 
 file_name = input（将这些数据保存为：）
 html_from_website = htmlfrom（www.stackoverflow.com）
 
打开（file_name，'w'）作为f：
 f.writ e（html_from_website）
  

解释

如果你在函数内部有导入语句，它只能在
函数内部访问（例如，其他函数无法访问它）

  import urllib.request 
  

PEP 8

a>指导如何在python中命名事物
CamelCase通常用于类名

  def htmlfrom（ website_url）：
'''
 docstring 
'''
  

Docstrings 通常是一个好主意。

查看此问题以获取有关正确使用全局的更多信息。
根据我所了解的情况，我认为您不需要使用它们。

  response = urllib .request.urlopen（website_url）
 variable_for_raw_data = response.read（）
 return variable_for_raw_data 
  

如果您不知道 if name ==' main '：您应该阅读它。

  if __name__ ==__main__：
  

不要忘记使用有意义的变量名称，不要覆盖
builtins （即file =foo.txt会覆盖内置文件）

  file_name = input（将这些数据保存为：）
 html_from_website = htmlfrom（www.stackoverflow.com）
  

您可以详细了解上下文管理器 here

 <作为f：
 f.write（html_from_website）
  

$带有open（file_name，'w'）的code> b $ b

使用 globals（）进行编辑，不存在任何用例存在。

  def htmlfrom（website_url）：
导入urllib.request 
响应= urllib.request.urlopen（website_url）
 variable_for_raw_data = （输入（将这些数据保存为：））
 globals（）[variable_for_raw_data] = response.read（）
  

I was wondering why I can't access the variable: "variable_for_raw_data" after the function ends. The code is like this:

def htmlfrom(Website_URL):
    import urllib.request
    response = urllib.request.urlopen(Website_URL)
    variable_for_raw_data =(input("What will this data be saved as: "))
    global variable_for_raw_data
    variable_for_raw_data = response.read()

Now why can't I access the variable "variable_for_raw_data" after the functions ends?

Things to note:

Python 3.3 urllib NOT urllib2

解决方案

It looks like you're trying to dynamically create variables, I would imagine that your code looks something like this.

def htmlfrom(website_url):
    import urllib.request
    response = urllib.request.urlopen(website_url)
    variable_for_raw_data =(input("What will this data be saved as: "))
    global variable_for_raw_data
    variable_for_raw_data = response.read()


if __name__ == "__main__":

    htmlfrom("www.stackoverflow.com")

    #html_stackoverflow is never created it is the value
    #of variable_for_raw_data before variable_for_raw_data
    #is overridden by response.read()

    #entering information into input doesn't create a variable
    print(html_stackoverflow)

Here's how I would do it:

import urllib.request

def htmlfrom(website_url): 
    '''
       docstrings
    '''

    response = urllib.request.urlopen(website_url)
    variable_for_raw_data = response.read()
    return variable_for_raw_data

if __name__ == "__main__":

    file_name = input("What will this data be saved as: ")
    html_from_website = htmlfrom("www.stackoverflow.com")

        with open(file_name, 'w') as f: 
        f.write(html_from_website)

Explanation

if you have your import statement inside the function it is only accessable inside the function (i.e. other functions can't access it)

import urllib.request

PEP 8 has guidelines on how things should be named in python CamelCase is usually reserved for class names

def htmlfrom(website_url): 
    '''
        docstring 
    '''

Docstrings are usually a good idea.

Check out this question for more information on the proper use of globals. Based on what I know about your situation I don't think you need to use them.

    response = urllib.request.urlopen(website_url)
    variable_for_raw_data = response.read()
    return variable_for_raw_data

If you don't know about `if name == 'main': you should read up on it.

if __name__ == "__main__":

Don't forget to use meaningful variable names and not override the builtins (i.e. file = "foo.txt" would override the file builtin)

    file_name = input("What will this data be saved as: ")
    html_from_website = htmlfrom("www.stackoverflow.com")

You can learn more about context managers here

    with open(file_name, 'w') as f: 
        f.write(html_from_website)

An edit using globals(), FOR WHICH NO USE CASE EXISTS AT ALL.

def htmlfrom(website_url):
    import urllib.request
    response = urllib.request.urlopen(website_url)
    variable_for_raw_data =(input("What will this data be saved as: "))
    globals()[variable_for_raw_data] = response.read()

这篇关于在函数中创建python 3中的全局变量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！