[Python] Using typeguard decorator: @typechecked in Python, whilst evading circular imports?

Context


To prevent circular imports in Python when using type-hints, one can use the following construct:

# controllers.py
from __future__ import annotations
from typing import TYPE_CHECKING

if TYPE_CHECKING:
from models import Book


class BookController:
def __init__(self, book: "Book") -> None:
self.book = book


Where the if TYPE_CHECKING: is only executed during type checking, and not during execution of the code.

Issue


When one applies active function argument type verification, (based on the type hints of the arguments), typeguard throws the error:

NameError: name 'Supported_experiment_settings' is not defined
​

MWE I


# models.py
from controllers import BookController

from typeguard import typechecked

class Book:

@typechecked
def get_controller(self, some_bookcontroller:BookController):
return some_bookcontroller

some_book=Book()
BookController("somestring")


And:

# controllers.py
from __future__ import annotations
from typing import TYPE_CHECKING
from typeguard import typechecked
#from models import Book

if TYPE_CHECKING:
from models import Book

class BookController:

@typechecked
def __init__(self, book: Book) -> None:
self.book = book


Note the #from models import Book is commented out. Now if one runs:

python models.py


It throws the error:

File "/home/name/Documents/eg/models.py", line 13, in BookController("somestring") ... NameError: name 'Book' is not defined. Did you mean: 'bool'? because the typechecking for def __init__(self, book: Book) -> None: does not know what the class Book is.
​

MWE II


Then if one disables @typechecked in controllers.py with:

# controllers.py
from __future__ import annotations
from typing import TYPE_CHECKING
from typeguard import typechecked

if TYPE_CHECKING:
from models import Book

class BookController:

#@typechecked
def __init__(self, book: Book) -> None:
self.book = book


it works. (But no typechecking).

MWE III


Then if one re-enables typechecking, and includes the import of book, (with from models import Book) like:

# controllers.py
from __future__ import annotations
from typing import TYPE_CHECKING
from typeguard import typechecked
from models import Book

if TYPE_CHECKING:
from models import Book

class BookController:

@typechecked
def __init__(self, book: Book) -> None:
self.book = book


It throws the circular import error:

Traceback (most recent call last):
File "/home/name/Documents/eg/models.py", line 2, in <module>
from controllers import BookController
File "/home/name/Documents/eg/controllers.py", line 5, in <module>
from models import Book
File "/home/name/Documents/eg/models.py", line 2, in <module>
from controllers import BookController
ImportError: cannot import name 'BookController' from partially initialized module 'controllers' (most likely due to a circular import) (/home/name/Documents/eg/controllers.py)

Question


How can one evade this circular import whilst still allowing the @typechecked decorator to verify/access the Book import?

Is there an equivalent TYPE_CHECKING boolean for typeguard?

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