pallets/flask · error · NoAppException

The factory {app_name!r} in module {module.__name__!r} could

Error message

The factory {app_name!r} in module {module.__name__!r} could not be called with the specified arguments.

What it means

Raised when the referenced attribute is a factory function and calling it with the arguments parsed from the CLI spec raises TypeError due to a signature mismatch (Flask checks via `_called_with_wrong_args` that the TypeError came from the call itself, not from inside the factory body). It means the arguments in `--app 'module:create_app(...)'` don't match the factory's parameters.

Source

Thrown at src/flask/cli.py:183

        )

    try:
        attr = getattr(module, name)
    except AttributeError as e:
        raise NoAppException(
            f"Failed to find attribute {name!r} in {module.__name__!r}."
        ) from e

    # If the attribute is a function, call it with any args and kwargs
    # to get the real application.
    if inspect.isfunction(attr):
        try:
            app = attr(*args, **kwargs)
        except TypeError as e:
            if not _called_with_wrong_args(attr):
                raise

            raise NoAppException(
                f"The factory {app_name!r} in module"
                f" {module.__name__!r} could not be called with the"
                " specified arguments."
            ) from e
    else:
        app = attr

    if isinstance(app, Flask):
        return app

    raise NoAppException(
        "A valid Flask application was not obtained from"
        f" '{module.__name__}:{app_name}'."
    )


def prepare_import(path: str) -> str:
    """Given a filename this will try to calculate the python path, add it

View on GitHub (pinned to 6a2f545bfd)

Solutions

1. Match the call in the spec to the factory signature, quoting literals: `flask --app 'app:create_app("development")' run`.
2. Give factory parameters defaults (`def create_app(config_name='development')`) so the bare `--app app:create_app` form works.
3. If the TypeError actually originates inside the factory (not the call), it is re-raised directly — read the traceback to distinguish; fix the factory's internal call instead.

Example fix

# before
flask --app 'myproj:create_app' run   # def create_app(config_name): ...
# after
flask --app 'myproj:create_app("development")' run

import inspect
from myproject import create_app
sig = inspect.signature(create_app)
sig.bind("dev")  # raises TypeError if ('dev') can't be passed

try:
    app = find_app_by_string(module, app_name)
except NoAppException as e:
    if e.__cause__ is not None:
        traceback.print_exception(e.__cause__)
    sys.exit(2)

When it happens

Trigger: `flask --app 'app:create_app'` (called with zero args) when `create_app(config_name)` has a required positional parameter; `flask --app 'app:create_app("dev", extra=1)'` when the factory takes no `extra` kwarg; passing the wrong number of positional literals.

Common situations: Adding a required parameter to an application factory without updating run scripts; expecting Flask to pass ScriptInfo automatically (legacy behavior removed in Flask 2.x — factories are now called with only the literals you specify); copying a `--app` string between projects with different factory signatures.

Related errors

• Detected factory '{attr_name}' in module '{module.__name__}'
• Detected multiple Flask applications in module '{module.__na
• Failed to find Flask application or factory in module '{modu
• Failed to parse {app_name!r} as an attribute name or functio
• Function reference must be a simple name: {app_name!r}.

AI-assisted analysis of pallets/flask@6a2f545bfd (2026-07-31). Data as JSON: /data/errors/3ebb98f849344918.json. Report an issue: GitHub.