Empty Body

What it does

Detects functions with empty bodies that have a non-None return type annotation.

The errors reported by this rule have the same motivation as the invalid-return-type rule. The diagnostic exists as a separate error code to allow users to disable this rule while prototyping code. While we strongly recommend enabling this rule if possible, users migrating from other type checkers may also find it useful to temporarily disable this rule on some or all of their codebase if they find it results in a large number of diagnostics.

Why is this bad?

A function with an empty body (containing only ..., pass, or a docstring) will implicitly return None at runtime. Returning None when the return type is non-None is unsound, and will lead to ty inferring incorrect types elsewhere.

Functions with empty bodies are permitted in certain contexts where they serve as declarations rather than implementations:

• Functions in stub files (.pyi)
• Methods in Protocol classes
• Abstract methods decorated with @abstractmethod
• Overload declarations decorated with @overload
• Functions in if TYPE_CHECKING blocks

Examples

def foo() -> int: ...  # error: [empty-body]


def bar() -> str:  # error: [empty-body]
    """A function that does nothing."""
    pass