Mypy can be challenging to use, but it is the most helpful Python static type checking tool that I have tried.Distribution of the py.typed file is now supported by Poetry ( python-poetry/poetry#1338). As explained in the mypy docs, an empty file named py.typed can be supplied with a package to indicate that the package supplies type information. PEP 561 introduced distribution methods for type information. See PEP 673 and what's new in Python 3.11. Update on type-annotating classes: Python 3.11 adds a Self type. Append a # type: ignore comment to the line. See the Mypy docs on implications of using Any. The most useful escape hatches to avoid dealing with this: Can modify class state (applies to other instances of the class) - Cannot modify object/instance state (the original class object definition). """Class method - accept `cls`, but not `self`. """ return "instance method called", self classmethod def class_method( cls) -> tuple: Can access the class itself (the original class object definition). """Class instance method - Class instance methods accept `self` as an argument. # No need for typing module imports after Python 3.9 # from typing import Tuple, Type, TypeVar # No need to explicitly declare TypeVar # T = TypeVar("T", bound="M圜lass") # Intuitive typing of instance and class methods class M圜lass: Real Python has provided a helpful tutorial on Python type checking, so I would refer you there to get started. Adding type annotations to source code Basics Other options include Pyright and the Pylance VSCode extension from Microsoft, and Pyre from Facebook. The most widely used tool to check static types is Mypy. Type annotations are also useful for data validation tools like Pydantic, which is used by FastAPI to generate an OpenAPI-compliant API schema. However, I have found that type-annotating my Python code helps me understand my code better, by encouraging me to think about the inputs and outputs of methods more thoroughly. I was skeptical at first, because dynamic typing is supposed to be a feature of Python, not a bug. I have found type annotations to be extremely useful. For some background on static typing, check out episode 151 of the Talk Python to Me podcast with Lukasz Langa, author of PEP 484 (and the Black autoformatter). PEP 484 added type annotations to Python. Static typing is becoming increasingly popular in dynamically typed languages. Adventures in the land of Python type annotations Table of Contents
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