Multiple Inheritance on Python

Question

how are you, people? I am facing this problem: I want to get all methods and attributes of 2 classes like the example below

class Person1:
      def __init__(self) -> None:
          self.john_name = "John"
          self.john_age = 36
  
      def get_name_john(self) -> str:
          return self.john_name
  
      def get_age_john(self) -> int:
          return self.john_age
  
  
class Person2:
      def __init__(self) -> None:
          self.ted_name = "Ted"
          self.ted_age = 32
 
      def get_name_ted(self) -> str:
          return self.ted_name
 
      def get_age_ted(self) -> int:
          return self.ted_age
 

class Student(Person1, Person2):
      def __init__(self) -> None:
          super().__init__()
          print(self.john_age)
          print(self.ted_age)
          print(self.get_name_john())
          print(self.get_name_ted())
          print(self.get_age_john())
          print(self.get_age_ted())
 
 
student = Student()

But when I do this I can't access anything from Person2. Maybe someone can help me with it? Thank you for your attention.

If you want to use super() with multiple inheritance, then every class has to use it - even the base classes. The alternative would be to explicitly call both parent class's __init__ methods from Student.__init__(). — jasonharper
– jasonharper, Commented Sep 6, 2022 at 22:55
Read the following: rhettinger.wordpress.com/2011/05/26/super-considered-super — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Sep 6, 2022 at 23:30

Brandon Li · Accepted Answer · 2022-09-07 02:42:42Z

1

You need to add super().__init__() to Person1 and Person2 as well. This is because of Method Resolution Order (MRO).

When __init__() is called in the Student class, the order at which to resolve __init__() is as follows:

Student -> Person1 -> Person2

Because __init__() is only called once, you would only be able to access Person1 which is one down the hierarchy.

After adding super().__init__() to both Person1 and Person2:

class Person1:
      def __init__(self) -> None:
          self.john_name = "John"
          self.john_age = 36
          super().__init__()
  
      def get_name_john(self) -> str:
          return self.john_name
  
      def get_age_john(self) -> int:
          return self.john_age
  
  
class Person2:
      def __init__(self) -> None:
          self.ted_name = "Ted"
          self.ted_age = 32
          super().__init__()
 
      def get_name_ted(self) -> str:
          return self.ted_name
 
      def get_age_ted(self) -> int:
          return self.ted_age
 

class Student(Person1, Person2):
      def __init__(self) -> None:
          super().__init__()
          print(self.john_age)
          print(self.ted_age)
          print(self.get_name_john())
          print(self.get_name_ted())
          print(self.get_age_john())
          print(self.get_age_ted())

The code now works.

answered Sep 7, 2022 at 2:42

Brandon Li

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3 Comments

Antonio Costa Over a year ago

Got it! If i just want to share a specific method of the 2 classes, for instance, just calling john_age from first class and ted_age from the second, I can do it as well, right?

Brandon Li Over a year ago

If you want to call a specific function from a parent class, you can just do super().function_name(). If that function exists in multiple parent classes, MRO will also apply, the same way it does here with __init__(). To change the order of MRO, you can simply change the order of the parent classes. For example you can swap the two classes around in Student(Person1, Person2), so that it would become Student(Person2, Person1), then the order of MRO would become Student -> Person2 -> Person1.

Antonio Costa Over a year ago

Got it! Thank you so much for the answer. I marked your answer as the correct one.

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