Why doesn't this work?
class Parent:
__var = "Whatever"
class Child(Parent):
def printVar(self):
print(self.__var)
Timmy = Child()
Timmy.printVar()
I get the following exception:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in printVar
AttributeError: 'Child' object has no attribute '_Child__var'
This is because you chose to name the attribute with a double leading underscore. This triggers some name-mangling
You can access it as self._Parent__var
In [8]: class Parent:
__var = "Whatever"
...:
In [9]: class Child(Parent):
def foo(self): print self._Parent__var
...:
In [10]: a=Child()
In [11]: a.foo()
Whatever
More information is available in the python docs at https://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references
You have provided __var as a class variable which is name-mangled due to the double-leading underscore. Hence, you cannot access it nicely with __var, but rather would need to use self._Parent__var. It can only be accessed by instances of Parent with __var, and not any sub-classes.
Hence, to still indicate that the attribute is private but avoid this name mangling, you may consider just using a single underscore.
class Parent:
_var = "Whatever"
class Child(Parent):
def printVar(self):
print(self._var)
Double underscore is used for private attributes, you should use single underscore.
class Parent:
_var = "Whatever"
class Child(Parent):
def printVar(self):
print(self._var)
Timmy = Child()
Timmy.printVar()
