verifyObject doesn't verify keyword arguments

[jluttine]

Given the following:

class IFoo(zope.interface.Interface):
    def bar(lorem="ipsum", alice=42):
        """ ... """

@zope.interface.implementer(IFoo)
class Foo():
    def bar(self, x=666, y=99):
        return x + y

I would have expected verification to fail but it doesn't:

>>> zope.interface.verify.verifyObject(IFoo, Foo())
True

How can I force verifyObject to verify the function signature exactly? So that it it is exactly the same (same positional and keyword arguments with same names in same order and also the same *args and **kwargs).

[d-maurer]

Jaakko Luttinen wrote at 2019-6-14 08:06 -0700:

Given the following: ``` class IFoo(zope.interface.Interface): def bar(lorem="ipsum", alice=42): """ ... """ @zope.interface.implementer(IFoo) class Foo(): def bar(self, x=666, y=99): return x + y ``` I would have expected verification to fail but it doesn't: ``` >>> zope.interface.verify.verifyObject(IFoo, Foo()) True ``` How can I force `verifyObject` to verify the function signature exactly? So that it it is exactly the same (same positional and keyword arguments with same names in same order and also the same `*args` and `**kwargs`).

A paramter definition of the form *param*=*value* can mean two things: 1. *param* is a positional parameter with default value *value* 2. *param* is a keyword argument For case 1, the parameter name has no importance (as positional parameters are identified via position, not via name). `zope.interface` cannot separate those two cases -- Python has only learned recently (Python 3+) to distinguish between those cases and `zope.interface` predates this. Because `zope.interface` cannot distinguish the cases, it is permissive (i.e. does not check the names). You will need your own verification in order to get the names checked. To help with its definition, you could make use of `dm.reuse.rebindFunction` (you find `dm.reuse` on PyPI): it allows you to reuse a function definition (`_verify`, `verifyClass` and `verifyObject`, all from `zope.interface.verify`, in this case) and change some of its "globals" (in your case `_incompat` and `_verify`). In your version of `_incompat` you would check in addition the parameter names. For a clean solution, `zope.interface` would need to learn how to differentiate between a positional argument with default value and a true keyword argument and check the names for the latter.

[icemac]

See #63 for some details. Maybe at least some parts of the issue can be fixed via a PR.

[d-maurer]

See #63 for some details. Maybe at least some parts of the issue can be fixed via a PR.

Will zope.interface drop Python 2 support soon?
After there is only Python 3, zope.interface should (of course) support Python 3's new keyword only arguments (and for them check that they do not change names).

I am against checking the names of positional arguments - whether with or without toggle: a positional argument is defined by its position not by its name. If I want an argument defined by name, I use a keyword only argument (provided I can do this because I support only Python 3).

[icemac]

From 2020-01-01 on there is no need to support Python 2.7 any more. (People needing Python 2 support can still use older package versions.)