Working with abstract base classes in Python
Jul 12, 2025 am 02:14 AMAbstract base class (ABC) is a tool used in Python to define interfaces. It is implemented through the abc module and cannot be instantiated. It must be inherited by subclasses and implements its abstract methods. 1. Use abc.ABC and @abstractmethod to define abstract methods to ensure that subclasses implement specific interfaces; 2. The abstract base class can contain specific methods for subclass inheritance; 3. Support multi-level inheritance to further refine abstract requirements; 4. Abstract properties can also be defined to force subclasses to implement attributes. It helps improve code readability, avoid runtime errors, and is suitable for building clear structured projects.
Abstract Base Classes (ABC) is a tool used to define interfaces in Python. It can help you write clearer and more structured code. If you are writing a class structure that needs to be inherited and extended, it will be helpful to use ABC well.

What is an abstract base class?
Simply put, an abstract base class is a class that cannot be instantiated. Its function is to define some methods that must be implemented by subclasses. Python's abc
module provides support, you can define abstract methods by inheriting ABC
class and using the @abstractmethod
decorator.
For example:

from abc import ABC, abstractmethod class Animal(ABC): @abstractmethod def make_sound(self): pass
This Animal
class is an abstract base class, you cannot create an Animal()
instance directly. Only subclasses that implement make_sound
method can be instantiated.
Why use abstract base classes?
- Force subclasses to implement specific methods : Ensure that all subclasses have consistent interfaces.
- Improve code readability : You can tell which methods must be implemented at a glance.
- Avoid runtime errors : If you forget to implement a method, an error will be reported when instantiated, rather than waiting until the actual call is done to discover the problem.
For example, if you write a program that deals with multiple animal sounds, if you do not force make_sound
, you may add an animal class one day but forget to write this method, and the program may make an error.

How to use abstract base classes correctly?
1. Use abc.ABC
and @abstractmethod
This is the most standard way. Inherit ABC
and add the @abstractmethod
decorator to the method to be enforced.
2. You can use a mixture of ordinary methods and abstract methods
There can be specific implementation methods in abstract base classes, and these methods will be inherited by subclasses. for example:
class Animal(ABC): @abstractmethod def make_sound(self): pass def sleep(self): print("Sleeping...")
In this way, all subclasses can call sleep()
directly.
3. Support multi-level inheritance
You can define an abstract subclass based on the abstract base class and continue to abstract. for example:
class Mammal(Animal): @abstractmethod def walk(self): pass
At this time, any class that implements Mammal
must implement make_sound
and walk
at the same time.
4. Abstract properties are also OK
In addition to methods, you can also require subclasses to implement properties:
class Animal(ABC): @property @abstractmethod def species(self): pass
Frequently Asked Questions and Notes
- Don't abuse abstract base classes : not every class requires abstraction. If you just want to organize your code, you don't have to use ABC.
- Cannot instantiate abstract classes : This is a mistake that is easy to make at the beginning, remember to only use subclasses.
- Can abstract methods be implemented? Not necessarily : Although not usually, you can also provide a default implementation, and subclasses can choose whether to override.
- Use it in conjunction with other mechanisms : for example, you can use
@classmethod
or@staticmethod
to cooperate withabstractmethod
.
In general, abstract base classes are a very practical tool, especially suitable for building projects with a certain hierarchy. If used well, it can make the code clearer and safer. Basically that's it.
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