📝 Python Docstring Guide – Google, NumPy, RST Formats Explained

🧲 Introduction – Why Are Docstrings Important?

Python is celebrated for its readability, and docstrings are central to that. A docstring is a special string that documents:

• 📦 What a module, function, class, or method does
• 🧪 What parameters it takes and returns
• 🧠 Why it exists and how to use it

Good docstrings improve code maintainability, enable automatic documentation tools like Sphinx, and make interactive help more useful.

🎯 In this guide, you’ll learn:

• How to write effective docstrings for modules, functions, classes
• Different docstring styles (Google, NumPy, reStructuredText)
• Real-world formatting examples
• Best practices and linting tools

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✅ What Is a Python Docstring?

A docstring is a string literal that appears as the first statement in a module, class, or function.

def greet(name):
    """Return a greeting message for the given name."""
    return f"Hello, {name}!"

📌 Accessible via help() or .__doc__.

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🧩 Docstring Types & Placement

📄 Module Docstring

"""math_utils.py - Utility functions for mathematical operations."""

Place this at the top of your .py file.

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🧱 Function Docstring

def add(a, b):
    """Add two numbers and return the result."""
    return a + b

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🏗️ Class and Method Docstring

class Car:
    """A simple car class."""

    def drive(self):
        """Simulate driving the car."""
        pass

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📐 Docstring Formatting Styles

✅ Google Style

def multiply(a: int, b: int) -> int:
    """
    Multiply two integers.

    Args:
        a (int): The first number.
        b (int): The second number.

    Returns:
        int: The product of a and b.
    """
    return a * b

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✅ NumPy Style

def divide(a, b):
    """
    Divide one number by another.

    Parameters
    ----------
    a : float
        Numerator.
    b : float
        Denominator.

    Returns
    -------
    float
        Result of the division.
    """
    return a / b

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✅ reStructuredText (RST) Style

def subtract(a, b):
    """
    Subtract two numbers.

    :param a: First number.
    :type a: int
    :param b: Second number.
    :type b: int
    :return: The difference.
    :rtype: int
    """
    return a - b

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🧰 Real-World Example – Document a CLI Tool

def parse_args():
    """
    Parse command-line arguments.

    Returns:
        argparse.Namespace: Parsed arguments.
    """
    ...

✅ Docstrings make CLI tools self-documenting and IDE-friendly.

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📘 Best Practices for Writing Docstrings

✅ Do This	❌ Avoid This
Use triple double-quotes (""")	Mixing quote styles
Start with a summary line	Jumping into details without overview
Write in present tense	Using past/future tense
Keep lines ≤ 72 characters	Writing unreadable blocks
Follow a consistent style guide	Mixing styles within a project

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🔍 Accessing Docstrings

✅ From Code

print(add.__doc__)

✅ Using help()

help(add)

✅ Works in Python REPL, IDEs, and Jupyter Notebooks.

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🧪 Tools to Enforce Docstring Quality

Tool	Purpose
pydocstyle	Checks PEP 257 compliance
flake8-docstrings	Lints inline with code rules
Sphinx	Generates full HTML docs

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📌 Summary – Recap & Next Steps

Python docstrings are a foundational part of writing clean, maintainable, and discoverable code. They’re not just for documentation—they’re tools for collaboration, introspection, and automation.

🔍 Key Takeaways:

• ✅ Docstrings document functions, classes, methods, and modules
• ✅ Use consistent formats like Google, NumPy, or reStructuredText
• ✅ Include parameters, returns, and brief descriptions
• ✅ Use help() and IDEs to view docstrings dynamically

⚙️ Real-World Relevance:
Essential for open-source packages, APIs, internal tools, and production-grade systems.

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❓ FAQ – Python Docstrings

❓ What’s the difference between a comment and a docstring?

✅ Comments (#) are for developers only.
✅ Docstrings ("""text""") are accessible at runtime via help() or introspection.

❓ Can a function work without a docstring?

✅ Yes, but it’s harder to understand, maintain, or generate documentation from it.

❓ Are docstrings part of the Python standard?

✅ Yes, standardized in PEP 257.

❓ How do I enforce docstring style?

✅ Use tools like pydocstyle, flake8-docstrings, or docformatter.

❓ What’s the best docstring style?

✅ Use Google or NumPy style for consistency and readability.

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