python builder design pattern unresolved reference error

Question

class AlgDispenser:

    # super class to output an algorithm out of a selection of algorithms
    def __init__(self, *algorithms: Algorithm):
        super().__init__()
        self._algs: list[Algorithm] = []
        self._activeAlg: int = 0
        for i in range(0, len(algorithms)):
            self._algs.append(algorithms[i])
            
    def addAlgorithm(self, alg: Algorithm) ->AlgDispenser:
        # builder pattern
        self._algs.append(alg)
        return  self

->AlgDispenser：由于某种原因向我展示了一个未解决的错误