how to assert that method accepts specific types

[Terry Reedy]

Darren Dale wrote:
> I would like to assert that a method accepts certain types. I have a
> short example that works:
> 
> from functools import wraps
> 
> def accepts(*types):
>     def check_accepts(f):
>         @wraps(f)
>         def new_f(self, other):
>             assert isinstance(other, types), \
>                 "arg %r does not match %s" % (other, types)
>             return f(self, other)
>         return new_f
>     return check_accepts
> 
> class Test(object):
> 
>     @accepts(int)
>     def check(self, obj):
>         print obj
> 
> t = Test()
> t.check(1)
> 
> but now I want Test.check to accept an instance of Test as well. Does
> anyone know how this can be accomplished? The following class
> definition for Test raises a NameError:
> 
> class Test(object):
> 
>     @accepts(int, Test)
>     def check(self, obj):
>         print obj

Because Test does not exist at the time the function is compiled.
Remove '@accepts...' and put Test.check = accepts(int, Test)(Test.check) 
after the class definition and it should work.

tjr