Better type hints for model_bakery.recipe

[hoefling]

Motivation

Using generic types in model_bakery.recipe module allows for better hints from IDEs (if supported). Generic types are part of the stdlib's typing since 3.5, so the changes are conform with the range of Python versions currently supported by the library (although note that 3.5 and 3.6 are EOL already).

Demo (Pycharm)

Demo (mypy)

Sample code snippet:

from django.db.models import Model, ForeignKey
from model_bakery.recipe import Recipe, foreign_key, related

class C(Model):
    ...

r = Recipe(C)

reveal_type(r)
reveal_type(r.extend(spam="eggs"))
reveal_type(r.make())
reveal_type(r.make(_quantity=None))
reveal_type(r.make(_quantity=100))
reveal_type(foreign_key(Recipe(C)))
reveal_type(related(r, r))

On current mainline, mypy will emit

test.py:14: note: Revealed type is "model_bakery.recipe.Recipe"
test.py:15: note: Revealed type is "model_bakery.recipe.Recipe"
test.py:16: note: Revealed type is "Union[django.db.models.base.Model, builtins.list[django.db.models.base.Model]]"
test.py:17: note: Revealed type is "Union[django.db.models.base.Model, builtins.list[django.db.models.base.Model]]"
test.py:18: note: Revealed type is "Union[django.db.models.base.Model, builtins.list[django.db.models.base.Model]]"
test.py:19: note: Revealed type is "model_bakery.recipe.RecipeForeignKey"
test.py:20: note: Revealed type is "model_bakery.recipe.related"

whereas with this PR, more fine-grained type hinting is made available:

test.py:14: note: Revealed type is "model_bakery.recipe.Recipe[test.C*]"
test.py:15: note: Revealed type is "model_bakery.recipe.Recipe[test.C]"
test.py:16: note: Revealed type is "test.C*"
test.py:17: note: Revealed type is "test.C*"
test.py:18: note: Revealed type is "builtins.list[test.C*]"
test.py:19: note: Revealed type is "model_bakery.recipe.RecipeForeignKey[test.C*]"
test.py:20: note: Revealed type is "model_bakery.recipe.related[test.C*]"

[hoefling]

Demo (pyre)

pyre doesn't support self-typing for an upper bound (which is admittedly not clearly specified by PEP 484), so it can't deduce the return type of Recipe.extend(). Everything else looks good here as well.

model_bakery/test.py:14:0 Revealed type [-1]: Revealed type for `r` is `Recipe[C]`.
model_bakery/test.py:15:0 Revealed type [-1]: Revealed type for `r.extend($parameter$spam = "eggs")` is `unknown`.
model_bakery/test.py:16:0 Revealed type [-1]: Revealed type for `r.make()` is `C`.
model_bakery/test.py:17:0 Revealed type [-1]: Revealed type for `r.make($parameter$_quantity = None)` is `C`.
model_bakery/test.py:18:0 Revealed type [-1]: Revealed type for `r.make($parameter$_quantity = 100)` is `typing.List[C]`.
model_bakery/test.py:19:0 Revealed type [-1]: Revealed type for `recipe.foreign_key(recipe.Recipe(test.C))` is `recipe.RecipeForeignKey[C]`.
model_bakery/test.py:20:0 Revealed type [-1]: Revealed type for `recipe.related(r, r)` is `related[C]`.

[timjklein36]

Before I kick off the CI workflows, please add an entry to the CHANGELOG.md.

[hoefling]

@timjklein36 done, also fixed issues reported by pre-commit.