<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def traverse_ingredients(self):
 """Recursively traverse this ingredient and its sub-ingredients. Yields ------ ingredient: sacred.Ingredient The ingredient as traversed in preorder. depth: int The depth of the ingredient starting from 0. Raises ------ CircularDependencyError: If a circular structure among ingredients was detected. """

        if self._is_traversing:
            raise CircularDependencyError(ingredients=[self])
        else:
            self._is_traversing = True
        yield self, 0
        with CircularDependencyError.track(self):
            for ingredient in self.ingredients:
                for ingred, depth in ingredient.traverse_ingredients():
                    yield ingred, depth + 1
        self._is_traversing = False