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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 cached_method(func):
 """ Memoize for class methods """

    @functools.wraps(func)
    def wrapper(self, *args):
        if not hasattr(self, "_cache"):
            self._cache = {}
        key = _argstring((func.__name__,) + args)
        if key not in self._cache:
            self._cache[key] = func(self, *args)
        return self._cache[key]
    return wrapper