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CreatorCallError

Symptom

modern_di.exceptions.resolution.CreatorCallError: Cannot resolve dependency chain:
  APP  Service (myapp.creator:7)
  caused by: Failed to call creator create_service: create_service() missing 1 required positional argument: 'port'. Check kwargs and skip_creator_parsing usage.
See: https://modern-di.modern-python.org/troubleshooting/creator-call-error/

It is raised at resolve time. .creator holds the creator, and .original_error holds the binding TypeError, which is also the exception's __cause__.

Cause

The arguments modern-di assembled, static kwargs plus resolved dependencies, do not fit the creator's signature. This usually comes from skip_creator_parsing=True, where nothing is wired by type and kwargs must supply every required argument. The TypeError then says which part is wrong:

  • missing 1 required positional argument: kwargs leaves out a required parameter.
  • got an unexpected keyword argument: kwargs has a key the creator does not take.
  • got some positional-only arguments passed as keyword arguments: kwargs names a positional-only parameter.

container.validate() cannot catch any of these, because with skip_creator_parsing=True there is no parsed signature to check kwargs against. Without skip_creator_parsing, an unknown key is rejected when the Factory is declared, as UnknownFactoryKwargError.

An exception raised inside the creator's body, a TypeError included, propagates as itself and is never wrapped in this error. A ResolutionError raised by a container.resolve() call in the body keeps its class too, and gains the creator's step in its .dependency_path, so its message draws the chain down to that creator.

Fix

Make kwargs cover exactly what the signature requires.

# Broken:
class Dependencies(Group):
    service = providers.Factory(
        create_service,
        scope=Scope.APP,
        skip_creator_parsing=True,
        bound_type=Service,
        kwargs={"host": "localhost"},
    )


Container(groups=[Dependencies]).resolve(Service)

# Works:
class Dependencies(Group):
    service = providers.Factory(
        create_service,
        scope=Scope.APP,
        skip_creator_parsing=True,
        bound_type=Service,
        kwargs={"host": "localhost", "port": 5432},
    )


assert isinstance(Container(groups=[Dependencies]).resolve(Service), Service)

See also