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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 get_instance(cls, instance_or_pk):
 """Return a model instance in ``db.session``. :param instance_or_pk: An instance of this model class, or a primary key. A composite primary key can be passed as a tuple. Example:: @db.atomic def increase_account_balance(account, amount):
 # Here `Account` is a subclass of `db.Model`. account = Account.get_instance(account) account.balance += amount # Now `increase_account_balance` can be # called with an account instance: increase_account_balance(my_account, 100.00) # or with an account primary key (1234):
 increase_account_balance(1234, 100.00) """


        if isinstance(instance_or_pk, cls):
            if instance_or_pk in cls._flask_signalbus_sa.session:
                return instance_or_pk
            instance_or_pk = inspect(cls).primary_key_from_instance(instance_or_pk)
        return cls.query.get(instance_or_pk)