Suppose I have an interface IDerived that's derived from an interface
IBase, overriding a field from it.
>>> from zope.interface import Interface
>>> from zope.schema import TextLine
>>> class IBase(Interface):
... a = TextLine(title=u"a")
... b = TextLine(title=u"b")
... c = TextLine(title=u"c")
>>> class IDerived(IBase):
... b = TextLine(title=u"b", default=u"B")
In this case, the field ordering of zope.schema means that I'll get
something like this:
>>> from zope.schema import getFieldNamesInOrder
['a', 'c', 'b']
I had rather expected the order to be ['a', 'b', 'c']. That is, I would
expect a field that overrides a field from a base interface, to retain
the base interface's order.
One way to fix this is to do:
>>> IDerived['b'].order = IBase['b'].order
Now both will have the same order, of course.
So, I'm wondering:
- Is it harmful to have two fields with the same order like this when
they share a name?
- Should this be the default behavior when deriving interfaces from
one another like this?
If the latter is desirable, I'd be willing to help find a way to
implement it. The field order is just an ever-increasing int that's set
in Field.__init__(), so we'd probably need some after-the-fact fixing up
One way to do that would be to fire an event at the end of
InterfaceClass.__init__() and have an event handler to fix the order,
though that'd make zope.interface dependent on zope.event which is
probably not desirable.
We could simulate the event handler in another way, of course, e.g. by
having the interface initialiser loop over its attributes and see if
they support e.g. an IOrderAware interface and call a method on it, and
have Field implement this.
What do you think?
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