Python inheritance returns attribute error

Question

Just starting out Python, i'm a fan of Derek Banas and have been following a tutorial and I'm stuck with a bit of code.

class Dog(Animal):
 __owner = ""
 def __init__(self, name, height, weight, sound, owner):
 self.__owner = owner
 super(Dog, self).__init__(name, height, weight, sound)
 def set_owner(self, owner):
 self.__owner = owner
 def get_owner(self):
 return self.__owner
 def get_type(self):
 print("Dog")
 def tostring(self):
 return "{} is {} cm tall and {} kilograms and say {} His owner is {}".format(self.__name,
 self.__height,
 self.__weight,
 self.__sound,
 self.__owner)
 def multiple_sounds(self, how_many=None):
 if how_many is None:
 print(self.get_sound())
 else:
 print(self.get_sound() * how_many)
spot = Dog("Spot", 53, 27, "Ruff", "Seb")
print(spot.tostring())

And i'm receiving the following error:

Traceback (most recent call last):
 File "G:/JetBrains/PyCharm Community Edition 4.5.4/PyCharm Projects/Testing 123/testing objects.py", line 87, in <module>
 print(spot.tostring())
 File "G:/JetBrains/PyCharm Community Edition 4.5.4/PyCharm Projects/Testing 123/testing objects.py", line 73, in tostring
 return "{} is {} cm tall and {} kilograms and say {} His owner is {}".format(self.__name,
AttributeError: 'Dog' object has no attribute '_Dog__name'

As I've previously transferred from programming with vb, the indentation for the format of the 'tostring' method baffles me a little bit. I even tried putting it all into one line and it still doesn't recognize the inherited attribute '__name' from the class Animal.

Help would be appreciated.

Edit:

It might be worth mentioning that i'm using Pycharm to write all this in.

Also here's the Animal class

class Animal:
 __name = ""
 __height = 0
 __weight = 0
 __sound = 0
 def __init__(self, name, height, weight, sound):
 self.__name = name
 self.__height = height
 self.__weight = weight
 self.__sound = sound
 def set_name(self, name):
 self.__name = name
 def set_height(self, height):
 self.__height = height
 def set_weight(self, weight):
 self.__weight = weight
 def set_sound(self, sound):
 self.__sound = sound
 def get_name(self):
 return self.__name
 def get_height(self):
 return self.__height
 def get_weight(self):
 return self.__weight
 def get_sound(self):
 return self.__sound
 def get_type(self):
 print("Animal")
 def tostring(self):
 return "{} is {} cm tall and {} kilograms and say {}".format(self.__name,
 self.__height,
 self.__weight,
 self.__sound)

• C.B.: Since name is set in the super, we would probably need to see the Animal code. As an aside, creating a tostring() method is rather un-pythonic, as you would want to look at overriding the __str__ and __repr__ magic methods.
• Alexis Lestrange: That's true, wasn't sure if it was necessary if what I said was that the attribute it was trying to find already exists in the super its inheriting, but I'll add the Animal class code to the original post.
• Daniel Roseman: If you've got this from a tutorial, you should get another one straight away. This is totally un-Pythonic code.

Answer 1

Your Animal class is using Name Mangling. From documentation -

Since there is a valid use-case for class-private members (namely to avoid name clashes of names with names defined by subclasses), there is limited support for such a mechanism, called name mangling. 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.

(Emphasis mine)

Hence , after your Animal class got defined any name such as __name would have changed to _Animal__name , etc. You would also need to access them alike that in your Dog class.

But I don't think you actually need to use Name Mangling , you should avoid using the two leading underscores, if you didn't mean for Name Mangling to happen.

• bgusach: In short: use a single trailing underscore, not double.
• Alexis Lestrange: Thanks, this seems to have worked. Is name mangling something that has been introduced within the last year? I ask this because inside the tutorial I was looking at they did not have any problems with using 2 underscores for their attributes.

Answer 2

Change your function code

from

def toString(self):
 return "{} is {} cm tall and {} kilograms and say {} and the owner is {}".format(
 self.__name,
 self.__height,
 self.__weight,
 self.__sound,
 self.__owner)

to

def toString(self):
 return "{} is {} cm tall and {} kilograms and say {} and the owner is {}".format(
 self.get_name(),
 self.get_height(),
 self.get_weight(),
 self.get_sound(),
 self.get_owner())

• toti08: Hi @Simon Neubauer, could you please add some more explanation to your answer?

Answer 3

The child class itself doesn't have the attribute, use this instead.

return super(Dog, self).toString() + "His owner is {}".format(self.__owner)