Learn how Mypy's type checking works with functions and generators.

Mypy can check more than simple Python types. In my last article, I introduced Mypy, a package that enforces type checking in Python programs. Python itself is, and always will remain, a dynamically typed language. However, Python 3 supports "annotations", a feature that allows you to attach an object to variables, function parameters and function return values. These annotations are ignored by Python itself, but they can be used by external tools.

Tighten up your code and identify errors before they occur with mypy. I've been using dynamic languages—Perl, Ruby and Python—for many years. I love the flexibility and expressiveness that such languages provide. For example, I can define a function that sums numbers: