类对象不继承其他类属性

Question

分为3类：患者，患者和医院。

class Patient:

    def __init__(self, ID, name, age, sex, alergies):
        self.ID = ID
        self.name = name
        self.age = age
        self.sex = sex
        self.alergies = alergies

    def Is_old(self):
        if self.age >= 60:
            return True
        else:
            return False

    def Add_patient(self, P):
        pass

class Patients():

    def __init__(self):
        self.dict = {}    # where key is a patient ID, value is an Patient object


class Hospital(Patients):

    def __init__(self, name):
        self.name = name

    def Get_oldPatients(self):
        old_patients = []
        for key, value in self.dict.items():   # where an error appears
            if Patient.Is_old():
                old_patients.append(value)
        return old_patients

出现错误

AttributeError: 'Hospital' object has no attribute 'dict'

医院类别是从患者那里继承的，因此应该具有与患者相同的属性，知道哪里出了问题吗？