__name__ attribute in python module

The __name__ attribute in python is a special variable:

1. __n name__ is a variable. The double underscores are added before and after because this is a system-defined name. Ordinary variables do not name variables this way.

2. Python has many modules, and these modules can run independently! This is not like C++ and C header files.

3. When importing, it is necessary to execute the imported module.

4. __name__ is a system variable that identifies the name of the module. There are two cases here: if the current module is the main module (that is, the module that calls other modules), then the name of this module is __main__, and the main function content after "__mian__:" can be executed by judging by if; if this module is If it is imported, the module name is the file name (without the following .py), and the content after "__mian__:" will be skipped by judging by if.

Through the above method, python can distinguish which are the main functions, enter the main function execution; and can call various functions of other modules and so on.

example:

# -*- coding: utf-8 -*-

' a test module ' # Documentation comments are accessible via __doc__

__author__ = 'frala' #author notes

import sys

def test():
      args = sys.argv
      if len(args)==1:
            print ('Hello world!')
      elif len (args) == 2:
            print ('Hello,%s' % args[1])
      else:
            print ('Too many arguments!')
            
if __name__ == '__main__':
      test()

Since this program is the main program, once executed

Because __name__ == '__main__', enter if, so the test function will be executed.

import hello

print (hello.__name__)

Now __name__=='hello' in the hello module, not '__main__' anymore.

So the hello module does not enter the if statement.