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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 add(self, name, mech, usage='both', init_lifetime=None, accept_lifetime=None, impersonator=None, store=None):
 """Acquire more credentials to add to the current set This method works like :meth:`acquire`, except that it adds the acquired credentials for a single mechanism to a copy of the current set, instead of creating a new set for multiple mechanisms. Unlike :meth:`acquire`, you cannot pass None desired name or mechanism. If the `impersonator` argument is used, the credentials will impersonate the given name using the impersonator credentials (:requires-ext:`s4u`). If the `store` argument is used, the credentials will be acquired from the given credential store (:requires-ext:`cred_store`). Otherwise, the credentials are acquired from the default store. The credential store information is a dictionary containing mechanisms-specific keys and values pointing to a credential store or stores. Note that the `store` argument is not compatible with the `impersonator` argument. Args: name (Name):
 the name associated with the credentials mech (OID):
 the desired :class:`MechType` to be used with the credentials usage (str):
 the usage for the credentials -- either 'both', 'initiate', or 'accept' init_lifetime (int):
 the desired initiate lifetime of the credentials, or None for indefinite accept_lifetime (int):
 the desired accept lifetime of the credentials, or None for indefinite impersonator (Credentials):
 the credentials to use to impersonate the given name, or None to not acquire normally (:requires-ext:`s4u`) store (dict):
 the credential store information pointing to the credential store from which to acquire the credentials, or None for the default store (:requires-ext:`cred_store`) Returns: Credentials: the credentials set containing the current credentials and the newly acquired ones. Raises: BadMechanismError BadNameTypeError BadNameError DuplicateCredentialsElementError ExpiredCredentialsError MissingCredentialsError """


        if store is not None and impersonator is not None:
            raise ValueError('You cannot use both the `impersonator` and '
                             '`store` arguments at the same time')

        if store is not None:
            if rcred_cred_store is None:
                raise NotImplementedError("Your GSSAPI implementation does "
                                          "not have support for manipulating "
                                          "credential stores")
            store = _encode_dict(store)

            res = rcred_cred_store.add_cred_from(store, self, name, mech,
                                                 usage, init_lifetime,
                                                 accept_lifetime)
        elif impersonator is not None:
            if rcred_s4u is None:
                raise NotImplementedError("Your GSSAPI implementation does "
                                          "not have support for S4U")
            res = rcred_s4u.add_cred_impersonate_name(self, impersonator,
                                                      name, mech, usage,
                                                      init_lifetime,
                                                      accept_lifetime)
        else:
            res = rcreds.add_cred(self, name, mech, usage, init_lifetime,
                                  accept_lifetime)

        return Credentials(res.creds)