WSGI Types for Python

This is an attempt to bring some type safety to WSGI applications using Python's new typing features (TypedDicts, Protocols). It seems to work OK but may still be full of gaps, holes, bugs, missteps, etc. It helped bring a lot of extra safety to a couple of places that really needed it though, and seemed to remain quite stable for a couple of months.

This is implemented as a Python module, rather than MyPy stubs, as it represents a protocol things can satisfy rather than a set of types for something concrete.

This package came together during an exploration documented here: https://github.com/python/mypy/issues/7654

Define a callable application as a class:

import wsgitypes

class MyApplication(wsgitypes.Application):
    def __call__(
        self,
        environ: wsgitypes.Environ,
        start_response: wsgitypes.StartResponse,
    ) -> wsgitypes.Response:
        my_header = environ.get("REQUEST_METHOD", "")
        return []

Environ should be type-safe:

class MyApplication(wsgitypes.Application):
    def __call__(
        self,
        environ: wsgitypes.Environ,
        start_response: wsgitypes.StartResponse,
    ) -> wsgitypes.Response:
        environ["wsgi.input"] # Good
        environ["wsgi.unpot"] # BORK! MyPy will catch this.
        return []

You can define your own extensions to Environ using TypedDict inheritance, like so:

class MyEnviron(wsgitypes.Environ):
    HTTP_X_MY_HEADER: t.Optional[str]

class MyApplication(wsgitypes.Application):
    def __call__(
        self,
        environ: MyEnviron,
        start_response: wsgitypes.StartResponse,
    ) -> wsgitypes.Response:
        environ = typing.cast(MyEnviron, environ)
        environ.get("HTTP_X_MY_HEADER") # Good
        return []

Note that you need to use typing.cast to convert the incoming Environ to your derived version. An attempt was made to use a type param for Environ, but it wasn't viable (even with GVR helping!): https://github.com/python/mypy/issues/7654

MyPy types for WSGI applications

Related tags

Overview

WSGI Types for Python

Owner

Blake Williams

:sparkles: Surface lint errors during code review

🦆 Better duck-typing with mypy-compatible extensions to Protocol

Flake8 extension for checking quotes in python

Tools for improving Python imports

Code audit tool for python.

Static Typing for Python

Simple Python style checker in one Python file

Utilities for refactoring imports in python-like syntax.

Flake8 Type Annotation Checking

Unbearably fast O(1) runtime type-checking in pure Python.

A python documentation linter which checks that the docstring description matches the definition.

Run isort, pyupgrade, mypy, pylint, flake8, and more on Jupyter Notebooks

A simple program which checks Python source files for errors

Mypy stubs, i.e., type information, for numpy, pandas and matplotlib

Flake8 wrapper to make it nice, legacy-friendly, configurable.

Reference implementation of sentinels for the Python stdlib

Flake8 plugin to find commented out or dead code

Static type checker for Python

Flake8 extension for enforcing trailing commas in python

A static type analyzer for Python code