Python Class Inheritance

Question

Think I might have misunderstood some of the concepts around inheritance.

This isn't related to a specific code challenge or video so I've created an example piece of code below:

class ParentClass:
     def __init__(self, first_name, last_name):
             self.first_name = first_name
             self.last_name = last_name

 class SubClass(ParentClass):
     def __init__(self, age, location):
             super().__init__(self)
             self.age = age
             self.location = location

 my_instance = SubClass(first_name="Joe", second_name="Bloggs", age=20, location="United Kingdom")

So I keep receiving a TypeError:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: __init__() got an unexpected keyword argument 'first_name'

As you can see I've overwritten the init method in SubClass as I wanted to add two new attributes (age, location), but then I've used super(). Shouldn't this allow me to specify first_name and last_name on the instance (my_instance) of SubClass?

Would be really grateful if anyone could offer me some help.

Answer 1 · 2019-06-10T16:11:08Z

June 10, 2019 4:11pm

Great work trying this on your own! The main issue is there isn't any place for the SubClass.__init__ to accept arguments that it would pass on to the ParentClass through the super() call. This where **kwargs is useful.

Rewriting you code (and correcting indentation issues):

>>> class ParentClass:
...      def __init__(self, first_name, last_name):
...              self.first_name = first_name
...              self.last_name = last_name
... 
>>> class SubClass(ParentClass):
...     def __init__(self, age, location, **kwargs):  # added **kwargs
...         super().__init__(**kwargs)  # supplying  **kwargs to parent __init__, do Not include 'self'
...         self.age = age
...         self.location = location
... 
>>> my_instance = SubClass(first_name="Joe", second_name="Bloggs", age=20, location="United Kingdom")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __init__
TypeError: __init__() got an unexpected keyword argument 'second_name'

# replacing second_name with last_name:
>>> my_instance = SubClass(first_name="Joe", last_name="Bloggs", age=20, location="United Kingdom")
>>> my_instance.__dict__
{'first_name': 'Joe', 'last_name': 'Bloggs', 'age': 20, 'location': 'United Kingdom'}

As when calling other methods, the self is not included when calling __init__

Post back if you have more questions. Good luck!!

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Python Class Inheritance

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