Python MRO

README.md

Python MRO

MRO (Method Resolution Order)

most of codes are referenced from https://tibetsandfox.tistory.com/26

basic.py

class Human:
    def say(self):
        print("Hello")
        
        
class Mother(Human):
    def say(self):
        print("Mother")
        
class Father(Human):
    def say(self):
        print("Father")
        

class Son(Father, Mother):
    pass

class Daughter(Mother, Father):
    pass
        

if __name__ == "__main__":
    print(Son.__mro__)
    """
    First printed object is high priority
    
    (
        <class '__main__.Son'>, # not implemented
        <class '__main__.Father'>, # <- implemented
        <class '__main__.Mother'>, 
        <class '__main__.Human'>, 
        <class 'object'>
    )
    """
    
    """
    Left inheritance is first
    """
    Son().say() # Father
    Daughter().say() # Mother

mixed-priority-error.py

class Human:
    pass
        
        
class Mother(Human):
    pass
        
class Father(Human):
    pass
        

class Son(Human, Father, Mother):
    pass

class Daughter(Mother, Father):
    pass
        

if __name__ == "__main__":
    """Describe mixed priority"""
    
    # No code described
    
    """
    Traceback (most recent call last):
    File "~/python-mro/main.py", line 15, in <module>
        class Son(Human, Father, Mother):
    TypeError: Cannot create a consistent method resolution
    order (MRO) for bases Human, Father, Mother
    """
    pass

priority.py

class Human:
    def say(self):
        print("Hello")
        
        
class Mother(Human):
    def say(self):
        super().say() # NOTE: use inherited method
        
class Father(Human):
    def say(self):
        print("Father")
        

class Son(Father, Mother):
    pass

class Daughter(Mother, Father):
    pass
        

if __name__ == "__main__":
    """Describe priority when multiple inheritance"""
    Son().say() # Father
    Daughter().say() # Father
    
    print(Son.__mro__)
    """
    (
      <class '__main__.Son'>, # not implemented
      <class '__main__.Father'>, # <- implemented
      <class '__main__.Mother'>, 
      <class '__main__.Human'>, 
      <class 'object'>
    )
    """
    print(Daughter.__mro__)
    """
    (
      <class '__main__.Daughter'>, # not implemented
      <class '__main__.Mother'>, # not implemented
      <class '__main__.Father'>, # <- implemented
      <class '__main__.Human'>, 
      <class 'object'>
    )
    """