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Abstract Factory in Python
Abstract Factory is a creational design pattern, which solves the problem of creating entire product families without specifying their concrete classes.
Abstract Factory defines an interface for creating all distinct products but leaves the actual product creation to concrete factory classes. Each factory type corresponds to a certain product variety.
The client code calls the creation methods of a factory object instead of creating products directly with a constructor call (new operator). Since a factory corresponds to a single product variant, all its products will be compatible.
Client code works with factories and products only through their abstract interfaces. This lets the client code work with any product variants, created by the factory object. You just create a new concrete factory class and pass it to the client code.
If you can’t figure out the difference between various factory patterns and concepts, then read our Factory Comparison.
Complexity:
Popularity:
Usage examples: The Abstract Factory pattern is pretty common in Python code. Many frameworks and libraries use it to provide a way to extend and customize their standard components.
Identification: The pattern is easy to recognize by methods, which return a factory object. Then, the factory is used for creating specific sub-components.
Conceptual Example
This example illustrates the structure of the Abstract Factory design pattern. It focuses on answering these questions:
- What classes does it consist of?
- What roles do these classes play?
- In what way the elements of the pattern are related?
main.py: Conceptual example
from __future__ import annotations
from abc import ABC, abstractmethod
class AbstractFactory(ABC):
"""
The Abstract Factory interface declares a set of methods that return
different abstract products. These products are called a family and are
related by a high-level theme or concept. Products of one family are usually
able to collaborate among themselves. A family of products may have several
variants, but the products of one variant are incompatible with products of
another.
"""
@abstractmethod
def create_product_a(self) -> AbstractProductA:
pass
@abstractmethod
def create_product_b(self) -> AbstractProductB:
pass
class ConcreteFactory1(AbstractFactory):
"""
Concrete Factories produce a family of products that belong to a single
variant. The factory guarantees that resulting products are compatible. Note
that signatures of the Concrete Factory's methods return an abstract
product, while inside the method a concrete product is instantiated.
"""
def create_product_a(self) -> AbstractProductA:
return ConcreteProductA1()
def create_product_b(self) -> AbstractProductB:
return ConcreteProductB1()
class ConcreteFactory2(AbstractFactory):
"""
Each Concrete Factory has a corresponding product variant.
"""
def create_product_a(self) -> AbstractProductA:
return ConcreteProductA2()
def create_product_b(self) -> AbstractProductB:
return ConcreteProductB2()
class AbstractProductA(ABC):
"""
Each distinct product of a product family should have a base interface. All
variants of the product must implement this interface.
"""
@abstractmethod
def useful_function_a(self) -> str:
pass
"""
Concrete Products are created by corresponding Concrete Factories.
"""
class ConcreteProductA1(AbstractProductA):
def useful_function_a(self) -> str:
return "The result of the product A1."
class ConcreteProductA2(AbstractProductA):
def useful_function_a(self) -> str:
return "The result of the product A2."
class AbstractProductB(ABC):
"""
Here's the the base interface of another product. All products can interact
with each other, but proper interaction is possible only between products of
the same concrete variant.
"""
@abstractmethod
def useful_function_b(self) -> None:
"""
Product B is able to do its own thing...
"""
pass
@abstractmethod
def another_useful_function_b(self, collaborator: AbstractProductA) -> None:
"""
...but it also can collaborate with the ProductA.
The Abstract Factory makes sure that all products it creates are of the
same variant and thus, compatible.
"""
pass
"""
Concrete Products are created by corresponding Concrete Factories.
"""
class ConcreteProductB1(AbstractProductB):
def useful_function_b(self) -> str:
return "The result of the product B1."
"""
The variant, Product B1, is only able to work correctly with the variant,
Product A1. Nevertheless, it accepts any instance of AbstractProductA as an
argument.
"""
def another_useful_function_b(self, collaborator: AbstractProductA) -> str:
result = collaborator.useful_function_a()
return f"The result of the B1 collaborating with the ({result})"
class ConcreteProductB2(AbstractProductB):
def useful_function_b(self) -> str:
return "The result of the product B2."
def another_useful_function_b(self, collaborator: AbstractProductA):
"""
The variant, Product B2, is only able to work correctly with the
variant, Product A2. Nevertheless, it accepts any instance of
AbstractProductA as an argument.
"""
result = collaborator.useful_function_a()
return f"The result of the B2 collaborating with the ({result})"
def client_code(factory: AbstractFactory) -> None:
"""
The client code works with factories and products only through abstract
types: AbstractFactory and AbstractProduct. This lets you pass any factory
or product subclass to the client code without breaking it.
"""
product_a = factory.create_product_a()
product_b = factory.create_product_b()
print(f"{product_b.useful_function_b()}")
print(f"{product_b.another_useful_function_b(product_a)}", end="")
if __name__ == "__main__":
"""
The client code can work with any concrete factory class.
"""
print("Client: Testing client code with the first factory type:")
client_code(ConcreteFactory1())
print("\n")
print("Client: Testing the same client code with the second factory type:")
client_code(ConcreteFactory2())
Output.txt: Execution result
Client: Testing client code with the first factory type:
The result of the product B1.
The result of the B1 collaborating with the (The result of the product A1.)
Client: Testing the same client code with the second factory type:
The result of the product B2.
The result of the B2 collaborating with the (The result of the product A2.)
