Cannot I declare an attribute with type in zope.interface?

Question

I'm using zope.interface module to declare an interface with some methods and attributes. Also, cannot I somehow declare not only the attribute names, but also their types?

from zope.interface import Interface, Attribute, implementer, verify

class IVehicle(Interface):
    """Any moving thing"""
    speed = Attribute("""Movement speed""") #CANNOT I DECLARE ITS TYPE HERE?
    def move():
        """Make a single step"""
        pass

score 1 · Answer 1 · answered May 30 '14 at 16:06

You can restrict the type of the attribute by introducing an invariant.

from zope.interface import Interface, Attribute, implementer, verify, invariant

def speed_invariant(ob):
    if not isinstance(ob.speed, int):
       raise TypeError("speed must be an int")

class IVehicle(Interface):
    """Any moving thing"""
    speed = Attribute("""Movement speed""")
    invariant(speed_invariant)

    def move():
        """Make a single step"""
        pass

your IVehicle class has a validateInvariants method you can call to validate none of the invariants are being broken in classes that implement it.

IVehicle.validateInvariants(vechile_instance)

I don't know of a way to specify the type of the Attribute directly, though.

Cannot I declare an attribute with type in zope.interface?

1 Answers1