What are some examples of using mypy in Python?

What are some examples of using mypy in Python?

Mypy is a static type checker for Python. Here are a few examples:

1. Basic Type Annotations:

   def greet(name: str) -> str:
       return f'Hello, {name}!'
   

   This function takes a string and returns a string.

2. Using Lists:

   from typing import List
   def total_length(names: List[str]) -> int:
       return sum(len(name) for name in names)
   

   This function takes a list of strings and returns the total length.

3. Optional Types:

   from typing import Optional
   def find_item(items: List[str], item: str) -> Optional[int]:
       try:
           return items.index(item)
       except ValueError:
           return None
   

   This function returns the index of an item or None if not found.

How do I run mypy on my Python files?

You can run mypy from the command line. First, install it using pip:

pip install mypy

Then, run it on your Python file:

mypy your_file.py

Can I use mypy with third-party libraries?

Yes, mypy can be used with third-party libraries that have type stubs. Many popular libraries provide type hints, and you can also create your own stubs if needed.