find_best_app() — flask Function Reference

Architecture documentation for the find_best_app() function in cli.py from the flask codebase.

Function python ApplicationCore Scaffolding calls 1 called by 1

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ApplicationCore→ Scaffolding→ find_best_app() — flask Function Reference

Dependency Diagram

graph TD
  61227b34_c67c_0bff_1c83_c375e071843e["find_best_app()"]
  a96499c3_f8a9_e782_f156_1c1ee4a86c69["cli.py"]
  61227b34_c67c_0bff_1c83_c375e071843e -->|defined in| a96499c3_f8a9_e782_f156_1c1ee4a86c69
  95e11cb3_caab_ad8f_3f8c_c26632862fe3["locate_app()"]
  95e11cb3_caab_ad8f_3f8c_c26632862fe3 -->|calls| 61227b34_c67c_0bff_1c83_c375e071843e
  c9d5aa34_1bf5_6777_6447_72b24ceb6b6b["_called_with_wrong_args()"]
  61227b34_c67c_0bff_1c83_c375e071843e -->|calls| c9d5aa34_1bf5_6777_6447_72b24ceb6b6b
  style 61227b34_c67c_0bff_1c83_c375e071843e fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

src/flask/cli.py lines 41–91

def find_best_app(module: ModuleType) -> Flask:
    """Given a module instance this tries to find the best possible
    application in the module or raises an exception.
    """
    from . import Flask

    # Search for the most common names first.
    for attr_name in ("app", "application"):
        app = getattr(module, attr_name, None)

        if isinstance(app, Flask):
            return app

    # Otherwise find the only object that is a Flask instance.
    matches = [v for v in module.__dict__.values() if isinstance(v, Flask)]

    if len(matches) == 1:
        return matches[0]
    elif len(matches) > 1:
        raise NoAppException(
            "Detected multiple Flask applications in module"
            f" '{module.__name__}'. Use '{module.__name__}:name'"
            " to specify the correct one."
        )

    # Search for app factory functions.
    for attr_name in ("create_app", "make_app"):
        app_factory = getattr(module, attr_name, None)

        if inspect.isfunction(app_factory):
            try:
                app = app_factory()

                if isinstance(app, Flask):
                    return app
            except TypeError as e:
                if not _called_with_wrong_args(app_factory):
                    raise

                raise NoAppException(
                    f"Detected factory '{attr_name}' in module '{module.__name__}',"
                    " but could not call it without arguments. Use"
                    f" '{module.__name__}:{attr_name}(args)'"
                    " to specify arguments."
                ) from e

    raise NoAppException(
        "Failed to find Flask application or factory in module"
        f" '{module.__name__}'. Use '{module.__name__}:name'"
        " to specify one."
    )