'Dissociates a subnet from a route table.
:param      subnet_association: The subnet association object or
subnet association ID.
:type       subnet_association: :class:`.EC2SubnetAssociation` or
``str``
:rtype:     ``bool``'

def ex_dissociate_route_table(self, subnet_association):

    if isinstance(subnet_association, EC2SubnetAssociation):
        subnet_association_id = subnet_association.id
    else:
        subnet_association_id = subnet_association
    params = {'Action': 'DisassociateRouteTable', 'AssociationId': subnet_association_id}
    res = self.connection.request(self.path, params=params).object
    return self._get_boolean(res)
