Python Docstrings

Python Docstring Rules

Use this skill when reviewing or writing Python docstrings.

Purpose and scope

• Use Google-style docstrings.
• Focus on public Python modules, classes, functions, and methods.
• Keep docstrings compact, specific, and easy to scan.

Request changes when

• a public API has no docstring;
• the summary line is vague or inaccurate;
• arguments, returns, or intentionally raised exceptions are undocumented;
• a non-trivial public API needs an example but does not have one.

Required structure

1. Short description
2. Optional longer explanation
3. Args
4. Returns
5. Optional Raises
6. Optional Example

Formatting rules

• Limit docstrings to 120 characters per line.
• In Args, use name (type): description.
• In Returns, describe both the type and meaning of the returned value.
• Add Raises when the function intentionally raises exceptions.
• Use doctest-style Example blocks with >>> when examples help clarify usage.

Reviewer checklist

• Is the docstring present on the public API?
• Is the summary line accurate?
• Are inputs, outputs, and exceptions documented?
• Would a user understand how to call this API from the docstring alone?

Example

def my_function(param1: int, param2: str = "default") -> bool:
    """Short description.

    A longer explanation.

    Args:
        param1 (int): Explanation of param1.
        param2 (str): Explanation of param2. Defaults to "default".

    Returns:
        bool: Explanation of the return value.

    Example:
        >>> my_function(1, "test")
        True
    """
    return True

Docstring for __init__ method

• Document constructor arguments in the class docstring rather than in a separate __init__ docstring.

class MyClass:
    """My class description.

    A longer explanation.

    Args:
        param1 (int): Description of param1.
        param2 (str): Description of param2.

    Example:
        >>> my_class = MyClass(param1=1, param2="test")
        >>> my_class.param1
        1
        >>> my_class.param2
        'test'
    """
    def __init__(self, param1: int, param2: str) -> None:
        ...