python 单下划线和双下划线

 underline.py
 __all__ = ['_underline_variable', '__underline_variable', '_underline_func',
            '__underline_func', '_underline_class', '__underline_class']

 _underline_variable = 100
 __underline_variable = 200

 def _underline_func():
     pass

 def __underline_func():
     pass

 class _underline_class():
     pass

 class __underline_class():
     pass

 class Base():
     def _underline(self):
         pass

     def __underline(self):  # 私有
         pass

 class Derived(Base):
     pass

 if __name__ == '__main__':
     base = Base()
     base._underline()
     #base.__underline()
     base._Base__underline()

     derived = Derived()
     derived._underline()
     #derived._Derived__underline()
     derived._Base__underline()

 test.py
 # 1 用import方式导入
 import underline

 print(underline._underline_variable)
 print(underline.__underline_variable)
 underline._underline_func()
 underline.__underline_func()
 test1 = underline._underline_class()
 test2 = underline.__underline_class()

 print('*' * 20)

 # 2 没有定义__all__属性,用from ... import *方式导入
 #from underline import *
 #print(_underline_variable)
 #print(__underline_variable)
 #_underline_func()
 #__underline_func()
 #test1 = _underline_class()
 #test2 = __underline_class()

 # 3 定义__all__属性,用from ... import *方式导入
 from underline import *
 print(_underline_variable)
 print(__underline_variable)
 _underline_func()
 __underline_func()
 test1 = _underline_class()
 test2 = __underline_class()