Why add a abstract method to __init__ method of abstract class as an attribute?

Question

I am reading a book about python design patterns. I feel a little puzzled When I see the code about 'factory' pattern.

class Profile(metaclass=ABCMeta):
    def __init__(self):
        self.sections = []
        **self.create_profile()**

    @abstractmethod
    def **create_profile**(self):
        pass

    def get_section(self):
        return self.sections

The method create_profile is a abstract method and it was add into init method. Please let me clear the reason that why do that.

Thanks a lot

Answer 1

• It means when you write a subclass to inherit Profile, you must override the abstract method.

A class that has a metaclass derived from ABCMeta cannot be instantiated unless all of its abstract methods are overridden.

example code:

from abc import ABCMeta, abstractmethod
class Profile(metaclass=ABCMeta):
    def __init__(self):
        self.sections = []
        self.create_profile()

    @abstractmethod
    def create_profile(self):
        pass

    def get_section(self):
        return self.sections
    
class SubProfile(Profile):
    def __init__(self):
       self.create_profile()

    def create_profile(self):
        self.sections = [1,2,3]

class AnotherSubProfile(Profile):
    def __init__(self):
       self.create_profile()

    def create_profile(self):
        self.sections = [4,5,6]

class NoCreateSubProfile(Profile):
    def __init__(self):
       self.sections = [7,8,9]
    
sub = SubProfile()
print(sub.get_section())
sub = AnotherSubProfile()
print(sub.get_section())
sub = NoCreateSubProfile()
print(sub.get_section())

result:

[1, 2, 3]
[4, 5, 6]
TypeError: Can't instantiate abstract class NoCreateSubProfile with abstract method create_profile

Edit: about why it was add into init method, I think it is just a simple example, so the book writer put the abstract method into init method so that you can call it when you create a object of the subclass to Profile without any extra actions that need to do.

• In other fancy words, create_profile in init may indicate Profile must be created first when the instance of Profile are created.
• create_profile not in init example:(basic the same to former one)

from abc import ABCMeta, abstractmethod
class Profile(metaclass=ABCMeta):
    def __init__(self):
        self.sections = []
        # self.create_profile()

    @abstractmethod
    def create_profile(self):
        pass

    def get_section(self):
        return self.sections
    
class SubProfile(Profile):
    def __init__(self):
        pass

    def create_profile(self):
        self.sections = [1,2,3]
    
sub = SubProfile()
sub.create_profile()
print(sub.get_section())