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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def collect(cls):
 """ Load all constant generators from settings.WEBPACK_CONSTANT_PROCESSORS and concat their values. """

        constants = {}

        for method_path in WebpackConstants.get_constant_processors():
            method = import_string(method_path)

            if not callable(method):
                raise ImproperlyConfigured('Constant processor "%s" is not callable' % method_path)

            result = method(constants)

            if isinstance(result, dict):
                constants.update(result)

        return constants