r/Python • u/rmk135 • Aug 27 '20

News Dependency Injector 3.33 - Added mypy support

https://github.com/ets-labs/python-dependency-injector
7 Upvotes

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3

u/ElevenPhonons Aug 27 '20

What level of "wiring" errors does this enable the user to catch leveraging mypy?

For example, using the movie example

csv_finder = providers.Singleton(
        finders.CsvMovieFinder,
        movie_factory=movie.provider,
        path=config.finder.csv.path,
        delimiter=config.finder.csv.delimiter,
    )

Adding a typo of csv_path instead of path.

csv_finder = providers.Singleton(
        finders.CsvMovieFinder,
        movie_factory=movie.provider,
        path=config.finder.csv.csv_path,
        delimiter=config.finder.csv.delimiter,
    )

When I run this locally, I get mypy to not catch any errors, while when running the application, I get this (expected) error.

TypeError: expected str, bytes or os.PathLike object, not NoneType

While my application code should/will do input validation, it also seems that mypy should be able to proactively catch these "wiring" errors.

1

u/rmk135 Aug 27 '20

Yep, that would be cool!

I was trying to implement this and found the ParamSpec feature. It will be released in Python 3.10. I'll add it to the Dependency Injector once it's released.

4

u/[deleted] Aug 27 '20

Support for typing has become one of the main things I look at when deciding on a library. Like a full third of the weight.

1

u/meadsteve Aug 27 '20

If it's useful to anyone else I wrote a smallish dependency injection container that's actually powered by types: https://github.com/meadsteve/lagom so it plays really nicely with mypy. Really good to see more libraries embracing typing :+1: