Abstract class

As explained in Software Design for Python Programmers

An abstract superclass is a superclass intended to define shared structure or required behavior without being instantiated directly.

An abstract class defines shared structure and required behavior without allowing direct instantiation. In Python, it derives from abc.ABC and declares required methods with @abstractmethod. Concrete subclasses must implement every abstract method; otherwise, they remain abstract. The superclass may also provide instance variables and reusable non-abstract methods. section 4.3.4

MotorVehicle, Car, and Truck

MotorVehicle requires start_engine() and stop_engine(), while supplying drive(), accelerate(), steering, and braking behavior. Car implements the required engine methods and inherits the rest. Truck implements them and overrides steering. Calling drive() on either concrete object reuses the superclass sequence while preserving vehicle-specific behavior. section 4.3.4 section 4.7

Figure 8.3 This version of the application is modeled from the Template Method Design Pattern. The abstract superclass GameReport outlines the steps in the proper order for the algorithm to generate a report. It implements the common steps _print_header() and _print_footer() and delegates the remaining steps _acquire_data(), _analyze_data(), and _print_report() to the BaseballReport and VolleyballReport subclasses. The public template method generate_report() in the superclass calls the step methods in the proper order. The grayed-out portions of the diagram haven’t changed logically from figures 8.1 and 8.2.

Shows an abstract GameReport superclass fixing report-generation order, implementing common steps, and delegating variable steps to subclasses. section 8.1.3

How Software Design for Python Programmers covers it

How deep it goes

Explains Python implementation, instantiation rules, inheritance, overrides, and a Template Method application.

Examples

Uses MotorVehicle with Car and Truck, plus GameReport with baseball and volleyball report subclasses.

What it assumes

Assumes classes and inheritance, while introducing abstract methods, concrete subclasses, and interfaces.

What you can do after

Build abstract Python hierarchies that share implementation while enforcing subclass-specific methods.

How it connects

Connects abstract classes with inheritance, concrete subclasses, interfaces, and the Template Method design pattern.

liveBookmanning.com

Read Software Design for Python Programmers on liveBook Get the book at manning.com

Also explained in

• 

  liveBookmanning.com
  .NET in Action, Second EditionAn abstract class is a C# class that may contain incomplete implementations and cannot be instantiated directly.
• 

  liveBookmanning.com
  Practices of the Python ProAn abstract base class is a class intended to define a common interface or behavior for subclasses and that may prevent direct instantiation until required methods are implemented.
• 

  liveBookmanning.com
  The Well-Grounded Python Developer: How the pros use Python and FlaskAn abstract class is a class intended to define shared structure or behavior without being instantiated directly.
• 

  liveBookmanning.com
  100 C++ Mistakes and How to Avoid ThemAn abstract base class is a C++ base class intended to define behavior for derived classes and not to be instantiated directly.
• 

  liveBookmanning.com
  Essential TypeScript 5, Third EditionAn abstract class is a class that can define shared members while preventing direct instantiation and requiring derived classes to implement designated abstract members.

Compare how 6 books explain abstract class →

Related concepts

• contractincludes · An API contract is a specification of the operations, data, and behavioral expectations that govern interactions between software components.
• classkind of · A class is a programming-language construct that defines a type’s structure or behavior and provides a basis for creating or representing objects.
• interfacecontrasts with · A software interface is a contract or boundary that specifies the operations, properties, or capabilities through which types or components interact, without requiring a particular implementation.
• abstractmethodconfigured by · abstractmethod is a decorator from Python's abc module that marks a method as abstract and requires concrete subclasses to implement it.

This explainer was generated by Manning's knowledge graph from the text of Software Design for Python Programmers. The section links point to the parts of the book it draws on.