Python object-oriented three access rights underline double underscore

One, double underline

If you want the internal properties to be inaccessible externally, you can add two underscores to the name of the property, and __ in Python, the variable name of the instance __ becomes a private variable (private), which can only be accessed internally and cannot be accessed externally.

is an instance variable that starts with a double underscore not necessarily externally accessible? Actually, it's not. cannot be accessed directly __name because the Python interpreter has changed the variable to the outside __name , so it is _Student__name still possible _Student__name to access the __name variable.

The external code can set the __name variable, but actually the variable __name and the variable inside the class are __name not a variable! The internal __name variables have been automatically changed by the Python interpreter _Student__name , and the external code has added a variable to the instance __name .

1>>>classStudent (object):2...def __init__(self, name):3.. self.__name=name4...defget_name (self):5...returnSelf.__name6...defset_name (self, name):7.. self.__name=name8 ... 9>>> st = Student ('Jack')Ten>>>St.get_name () One 'Jack' A>>> St.set_name ('Mike') ->>>St.get_name () - 'Mike' the>>>dir (ST) -['_student__name','__class__','__delattr__','__dict__','__dir__','__doc__','__eq__','__format__','__ge__','__getattribute__','__gt__','__hash__','__init__','__le__','__lt__','__module__','__ne__','__new__','__reduce__','__reduce_ex__','__repr__','__setattr__','__sizeof__','__str__','__subclasshook__','__weakref__','get_name','Set_name'] ->>> St.__name - Traceback (most recent): +File"<stdin>", Line 1,inch<module> -Attributeerror:'Student'object has no attribute'__name' +>>>St._student__name A 'Mike' at>>> St.__name='New'   #added a new variable to the instance ->>> St.__name  - 'New' ->>>St._student__name - 'Mike'

Two, single underline

There are times when you see an instance variable name that starts with an underscore, such as an _name instance variable that can be accessed externally, but, as you see in the rules, when you look at a variable like this, the meaning is, "although I can be accessed, please treat me as a private variable and don't feel free to access it."

 1  >>> class   Student (object):  2  ... def  __init__   (self, name):   3  ... self._name = name  4   ...  5  >>> st = Student ( " jack  "  )  6  >>> st._name   7   " jack   " 

Third, special variables

A variable that starts with a double underscore and ends with a double underscore, and the special variable is directly accessible, not a private variable.

1>>>classStudent (object):2...def __init__(self, name):3.. self.__name=name4...defget_name (self):5...returnSelf.__name6 ... 7>>> st = Student ('Jack')8>>>St.get_name ()9 'Jack'Ten>>> St.__init__('Mike') One>>>St.get_name () A 'Mike'

Python object-oriented three access rights underline double underscore