Function validate_background_callbacks

dash/_validate.py:535–564

(callback_map)

def validate_background_callbacks(callback_map):
    # Validate that background callback side output & inputs are not circular
    # If circular, triggering a background callback would result in a fatal server/computer crash.
    all_outputs = set()
    input_indexed = {}
    for callback in callback_map.values():
        out = coerce_to_list(callback["output"])
        all_outputs.update(out)
        for o in out:
            input_indexed.setdefault(o, set())
            input_indexed[o].update(coerce_to_list(callback["raw_inputs"]))

    for callback in (x for x in callback_map.values() if x.get("background")):
        bg_info = callback["background"]
        progress = bg_info.get("progress", [])
        running = bg_info.get("running", [])

        bg_inputs = coerce_to_list(callback["raw_inputs"])
        outputs = set([x[0] for x in running] + progress)
        circular = [
            x
            for x in set(k for k, v in input_indexed.items() if v.intersection(outputs))
            if x in bg_inputs
        ]

        if circular:
            raise exceptions.BackgroundCallbackError(
                f"Background callback circular error!\n{circular} is used as input for a background callback"
                f" but also used as output from an input that is updated with progress or running argument."
            )


def validate_duplicate_output(