fix-mypy

Fix MyPy Type Errors

Systematic workflow for fixing MyPy type checking errors in the codebase.

Usage

/fix-mypy

Current Status

• MyPy: Currently DISABLED in pre-commit due to 145+ errors
• Goal: Fix all errors to enable strict type checking
• Target: 0 errors (100% type safety)
• Checklist: See .github/checklists/TYPE_SAFETY_MIGRATION.md

Quick Start

Run MyPy to See Errors

mypy src/ --show-error-codes

Run on Specific Module

mypy src/mcp_server_langgraph/core/config.py

Save Errors to File

mypy src/ --show-error-codes > mypy_errors.txt

Common Error Types & Fixes

1. Missing Return Type Annotation

Error: error: Function is missing a return type annotation

# ❌ Before
def get_user(user_id: str):
    return user_service.get(user_id)

# ✅ After
def get_user(user_id: str) -> User | None:
    return user_service.get(user_id)

2. Missing Type Hints for Function Arguments

Error: error: Function is missing a type annotation for one or more arguments

# ❌ Before
def process_data(data):
    return data.upper()

# ✅ After
def process_data(data: str) -> str:
    return data.upper()

3. Incompatible Types in Assignment

Error: error: Incompatible types in assignment (expression has type "X", variable has type "Y")

# ❌ Before
result: int = get_value()  # get_value() returns str

# ✅ After - Option 1: Fix type hint
result: str = get_value()

# ✅ After - Option 2: Convert type
result: int = int(get_value())

4. Optional Not Handled

Error: error: Item "None" of "Optional[X]" has no attribute "Y"

# ❌ Before
config = get_config()  # Returns Optional[Config]
value = config.get("key")  # MyPy error

# ✅ After
config = get_config()
if config is not None:
    value = config.get("key")

5. Argument Type Mismatch

Error: error: Argument 1 has incompatible type "X"; expected "Y"

# ❌ Before
def process(data: dict) -> None:
    ...

process([1, 2, 3])  # Passing list instead of dict

# ✅ After
process({"key": "value"})  # Pass correct type