L07 Class Comments

title: "Class Comments — Documenting Object-Oriented Code Interfaces" weight: 7 description: "Learn how to write class comments and docstrings that document object-oriented interfaces. Master class-level documentation covering attributes, methods, inheritance, and usage patterns for maintainable OOP code." date: 2026-06-28 lastmod: 2026-06-28 tags: [technical-writing, code-comments]

Class comments document the purpose and interface of a class. They explain what the class represents, how it should be used, and how it fits into the larger system.

In this lesson, you will learn how to write effective class-level documentation.

## What You'll Learn

You will write class docstrings that document purpose, attributes, and usage patterns.

## Why It Matters

Classes encapsulate data and behavior. Good class documentation tells developers what the class represents and how to use it without reading every method.

## Real-World Use

DodaTech class docstrings follow a standard template: class purpose, attribute documentation, usage example, and notes on thread safety or inheritance.

```mermaid
flowchart LR
  A[Class Comment] --> B[Purpose]
  A --> C[Attributes]
  A --> D[Usage Example]
  A --> E[Thread Safety]
  A --> F[Inheritance Notes]
  B --> G[Complete Interface]
  A:::current
  classDef current fill:#f90,color:#fff,stroke:#333,stroke-width:2px

Class Docstring Structure

Start with a description of what the class represents and its primary responsibility.

Document all public attributes with their types and descriptions. Include initialization requirements.

Include a usage example showing how to instantiate and use the class.

Document thread safety characteristics. Is the class thread-safe? Should external synchronization be used?

Document inheritance expectations if the class is designed to be subclassed.

class Compressor:
    """Compress files using configurable algorithms and streaming.

    The Compressor class provides the main interface for file compression.
    It supports gzip, bzip2, and xz algorithms with configurable levels.

    Attributes:
        algorithm: The compression algorithm to use.
        level: Compression level from 1 to 9.
        block_size: Size of streaming blocks in bytes.

    Example:
        compressor = Compressor(algorithm="gzip", level=6)
        result = compressor.compress_file("data.csv")

    Note:
        This class is thread-safe for independent file operations.
        Sharing a single Compressor instance across threads is safe
        as long as different files are being compressed.
    """

    def __init__(self, algorithm: str = "gzip", level: int = 6):
        self.algorithm = algorithm
        self.level = level
        self.block_size = 64 * 1024

Documenting Class Patterns

Document design patterns used in the class. If it is a factory, singleton, or strategy pattern, say so.

Document dependencies the class requires. What other classes or services must be available?

Document lifecycle expectations. Does the class need setup before use? Does it need cleanup after?

class CompressionFactory:
    """Factory for creating Compressor instances.

    This factory follows the Factory Method pattern. It creates the
    appropriate Compressor subclass based on the algorithm name.

    Usage:
        factory = CompressionFactory()
        compressor = factory.create("gzip")
        result = compressor.compress_file("data.csv")

    The factory caches compressor instances. Calling create with the
    same algorithm returns the same instance.
    """

Common Mistakes

1. No Class Docstring

Classes without purpose documentation. Developers must read all methods to understand the class.

2. Only Method Documentation

Documenting methods but not the class itself. The class purpose is unclear.

3. No Attribute Documentation

Class attributes without descriptions. Developers must guess what each attribute represents.

4. No Usage Example

Class docstrings without examples. Developers must piece together usage from method documentation.

5. Missing Thread Safety Notes

Not documenting whether the class is thread-safe. Developers may introduce bugs by sharing instances.

6. Documenting Private Implementation

Class docstrings that expose internal implementation details. Document the public interface.

7. Out of Date

Class docstrings that describe old behavior after refactoring.

Practice Questions

1. What should a class docstring include?

Purpose, attributes, usage example, thread safety notes, and inheritance expectations.

2. Why include a usage example in the class docstring?

The example shows how to instantiate and use the class. It is faster than reading method documentation.

3. Why document thread safety?

Developers need to know whether they can share instances across threads. Thread-safety bugs are hard to debug.

4. What is the difference between documenting a class and its methods?

The class docstring explains what the class represents. Method docstrings explain individual operations.

5. Challenge: Write a complete class docstring for a class you use. Include purpose, attributes, usage example, and thread safety notes.

FAQ

Mini Project

Audit a codebase's class documentation. Find three classes without docstrings or with incomplete docstrings. Write complete class docstrings for each following the template from this lesson.

What's Next

Next: Module Comments