Enhance Code Reliability with Mypy Type Checking

This challenge focuses on integrating static type checking into a Python project using MyPy. Static type checking helps catch a significant class of bugs early in the development cycle by verifying type consistency before code execution. You will be tasked with setting up MyPy and resolving type errors in a provided code snippet.

Problem Description

Your task is to make a given Python script fully compliant with MyPy's static type checking. This involves:

• Installing MyPy: If not already installed.
• Running MyPy: Executing MyPy against the provided Python code.
• Resolving Type Errors: Identifying and fixing all type-related errors reported by MyPy. This might involve adding type annotations, adjusting function signatures, or correcting existing type usage.
• Ensuring a Clean Run: The ultimate goal is to run MyPy on your modified code and receive no error output, indicating that all type annotations are consistent.

Key Requirements:

• The provided Python script must be runnable after your modifications.
• MyPy must report zero errors when run against the final version of the script.
• Do not introduce significant changes to the core logic or functionality of the script. The focus is solely on type correctness.

Expected Behavior:

When MyPy is executed on your corrected code, it should exit with a status code of 0 and produce no output on stderr.

Edge Cases to Consider:

• Complex Type Hinting: Be prepared to handle more intricate type hints like Optional, Union, List, Dict, and custom TypedDict if they are present or become necessary.
• Third-Party Libraries: If the script uses external libraries, you might need to ensure you have their corresponding type stubs installed (e.g., pip install mypy-extensions or pip install types-requests).

Examples

Example 1: Basic Type Annotation and Error Correction

# Original Code (before your modifications)
def greet(name):
    return f"Hello, {name}!"

message = greet(123)
print(message)

MyPy Output (Illustrative):

main.py:3: error: Argument 1 to "greet" of "..." has incompatible type "int"; expected "str"  [arg-type]
main.py:5: error: Cannot infer type of ...  [possibly-undefined]
Found 2 errors in 1 file (checked 1 source file)

Your Task: Modify the code to include type annotations and correct the call to greet.

Corrected Code (Illustrative Output):

# Your Corrected Code
def greet(name: str) -> str:
    return f"Hello, {name}!"

message: str = greet("Alice")
print(message)

MyPy Output (After your corrections):

# No output, indicating success

Explanation: The original greet function accepted any type for name, but was intended to work with strings. The call greet(123) passed an integer. By adding the type hint name: str to the function signature and message: str to the variable, and by correcting the call to greet("Alice"), MyPy can now verify type consistency.

Example 2: Handling Optional Types

# Original Code (before your modifications)
def get_user_id(username):
    if username == "admin":
        return 1
    else:
        return None

user_id = get_user_id("guest")
if user_id:
    print(f"User ID: {user_id}")
else:
    print("User not found.")

MyPy Output (Illustrative):

main.py:2: error: Missing return type annotation for "get_user_id"  [no-untyped-def]
main.py:6: error: Unsupported operand types for == ("None" and "str")  [operator]
Found 2 errors in 1 file (checked 1 source file)

Your Task: Add type hints, including for optional return values, and fix type incompatibilities.

Corrected Code (Illustrative Output):

# Your Corrected Code
from typing import Optional

def get_user_id(username: str) -> Optional[int]:
    if username == "admin":
        return 1
    else:
        return None

user_id: Optional[int] = get_user_id("guest")
if user_id is not None: # More explicit check for None
    print(f"User ID: {user_id}")
else:
    print("User not found.")

MyPy Output (After your corrections):

# No output, indicating success

Explanation: The get_user_id function could return either an integer or None. This is represented by Optional[int]. The comparison username == "admin" was also problematic because username's type wasn't explicitly defined, and get_user_id("guest") returned None, which MyPy flagged in the if user_id: check (though the explicit is not None is a clearer Pythonic way and also resolves MyPy warnings).

Constraints

• The provided Python script will be Python 3.8 or later.
• The script will not rely on overly obscure or highly experimental Python features.
• You are expected to use standard MyPy configurations. No advanced or custom plugins are required.
• The primary focus is on correctness of type hints and adherence to MyPy's findings, not on optimizing runtime performance.

Notes

• You will be provided with a Python script file (e.g., main.py). Your task is to modify this file in place or create a new corrected version.
• The goal is to achieve a successful MyPy run with no errors reported.
• Familiarize yourself with common type hints like str, int, float, bool, List, Dict, Tuple, Set, Optional, and Union.
• Use mypy your_script_name.py to run the checks.
• Consider using a type checking configuration file (mypy.ini or pyproject.toml) for more complex projects, though for this challenge, direct execution might suffice.
• Remember that type checking happens statically; it does not affect the runtime behavior of your code, but it drastically improves its robustness and maintainability.