reportMissingParameterType.md

April 8, 2026 · View on GitHub

Overview

reportMissingParameterType is a diagnostic in Pylance and Pyright that warns when a function or method parameter is missing a type annotation. This helps catch missing or ambiguous type information, improving code clarity and type safety.

Representative Issues

  • #3078: Always provide type hints for function parameters to avoid diagnostic errors in static analysis tools.
  • #2735: Provide specific configuration options for type check diagnostics to improve code maintainability.
  • #774: When using decorators that modify the signature of a function, use TypeVars bound to Callable types to maintain the original signatures.

Examples

def greet(name):  # Warning: Type of parameter "name" is unknown
    print(f"Hello, {name}")

def add(a, b):  # Warning: Type of parameter "a" is unknown
    return a + b

Fix — add type annotations to parameters:

def greet(name: str) -> None:
    print(f"Hello, {name}")

def add(a: int, b: int) -> int:
    return a + b

Common Fixes & Workarounds

  1. Add explicit type annotations to all function and method parameters.
  2. Use type stubs or install third-party stubs for external libraries.
  3. Review and update type hints in your codebase for completeness.
  4. Review the Pyright configuration documentation for options to adjust or suppress this diagnostic if needed.

See Also