| from zope.interface import invariant | |
| def required_contact(obj): | |
| if not (obj.email or obj.phone): | |
| raise Exception("At least one contact info is required") | |
| class IPerson(Interface): | |
| name = Attribute("Name") | |
| email = Attribute("Email Address") | |
| phone = Attribute("Phone Number") | |
| invariant(required_contact) | |