<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def construct(self, sp_entity_id, attrconvs, policy, issuer, farg, authn_class=None, authn_auth=None, authn_decl=None, encrypt=None, sec_context=None, authn_decl_ref=None, authn_instant="", subject_locality="", authn_statem=None, name_id=None, session_not_on_or_after=None):
 """ Construct the Assertion :param sp_entity_id: The entityid of the SP :param in_response_to: An identifier of the message, this message is a response to :param name_id: An NameID instance :param attrconvs: AttributeConverters :param policy: The policy that should be adhered to when replying :param issuer: Who is issuing the statement :param authn_class: The authentication class :param authn_auth: The authentication instance :param authn_decl: An Authentication Context declaration :param encrypt: Whether to encrypt parts or all of the Assertion :param sec_context: The security context used when encrypting :param authn_decl_ref: An Authentication Context declaration reference :param authn_instant: When the Authentication was performed :param subject_locality: Specifies the DNS domain name and IP address for the system from which the assertion subject was apparently authenticated. :param authn_statem: A AuthnStatement instance :return: An Assertion instance """


        if policy:
            _name_format = policy.get_name_form(sp_entity_id)
        else:
            _name_format = NAME_FORMAT_URI

        attr_statement = saml.AttributeStatement(attribute=from_local(
            attrconvs, self, _name_format))

        if encrypt == "attributes":
            for attr in attr_statement.attribute:
                enc = sec_context.encrypt(text="%s" % attr)

                encd = xmlenc.encrypted_data_from_string(enc)
                encattr = saml.EncryptedAttribute(encrypted_data=encd)
                attr_statement.encrypted_attribute.append(encattr)

            attr_statement.attribute = []

        # start using now and for some time
        conds = policy.conditions(sp_entity_id)

        if authn_statem:
            _authn_statement = authn_statem
        elif authn_auth or authn_class or authn_decl or authn_decl_ref:
            _authn_statement = authn_statement(authn_class, authn_auth,
                                               authn_decl, authn_decl_ref,
                                               authn_instant,
                                               subject_locality,
                                               session_not_on_or_after=session_not_on_or_after)
        else:
            _authn_statement = None

        subject = do_subject(policy, sp_entity_id, name_id,
                             **farg['subject'])

        _ass = assertion_factory(issuer=issuer, conditions=conds,
                                 subject=subject)

        if _authn_statement:
            _ass.authn_statement = [_authn_statement]

        if not attr_statement.empty():
            _ass.attribute_statement = [attr_statement]

        return _ass