Static Type Checker

In Python, a static type checker is a tool that analyzes your code without executing it to ensure that the types of variables and expressions are consistent with their annotations or type hints. This process, known as static type checking, helps you catch potential bugs early in the development process by verifying that your code adheres to the expected types.

Python’s dynamic nature allows for flexible and rapid development, but it also increases the risk of runtime type errors. By using a static type checker, you can leverage the benefits of both dynamic and static typing.

The mypy tool is a popular static type checker that checks your code against type hints. When you run mypy on your code, it will provide feedback on any type of inconsistencies it detects, helping you maintain type safety and improve code quality.

Example

Here’s an example of how you might the mypy static type checker to check your Python code:

Python 
def greet(name: str) -> str:
    return "Hello, " + name

greet("Alice")
greet(42)

In this example, mypy will flag the second call to greet() as an error because 42 is an integer, not a string. This helps catch potential issues before the code runs.

The Ultimate Guide to Python Type Checking

Tutorial

Python Type Checking (Guide)

In this guide, you'll look at Python type checking. Traditionally, types have been handled by the Python interpreter in a flexible but implicit way. Recent versions of Python allow you to specify explicit type hints that can be used by different tools to help you develop your code more efficiently.

intermediate best-practices

For additional information on related topics, take a look at the following resources:

By Leodanis Pozo Ramos • Updated Jan. 2, 2025 • Reviewed by Dan Bader
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