Python attribute error object has no attribute

问题:

When I apply two underscores I get the error AttributeError: 'Organization' object has no attribute '__employees' Here is the code.

 class Organization(object):
        __employees=[]

    google=Organization()
    google.__employees.append('Erik')

Python doesn't implement private variable concept. If so what I get error. If I remove one underscore code execute without an error.

回答1:

Well you have declared it as a private variable.

>>> class Organization(object):
...     __employees = []
... 
>>> google = Organization()
>>> google._Organization__employees.append('Erik')
>>> google._Organization__employees
['Erik']

>>> dir(Organization)
['_Organization__employees', '__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']

As you can see it save your vairable name with _Classname__Variablename. In your case it is _Organization__employees.

From the Python docs:

Any identifier of the form __spam (at least two leading underscores, at most one trailing underscore) is textually replaced with _classname__spam, where classname is the current class name with leading underscore(s) stripped. This mangling is done without regard to the syntactic position of the identifier, so it can be used to define class-private instance and class variables, methods, variables stored in globals, and even variables stored in instances. private to this class on instances of other classes.