Python - isinstance() not working as I'd expect

Question

I have a class called Route (with its own __repr__() function), and an instance of a Route called default_route. However, if I call isinstance(default_route,Route), it unexpectedly returns False, viz:

[Dbg]>>> default_route
Route(office(235)=323-654-3242)
[Dbg]>>> isinstance(default_route,Route)
False
[Dbg]>>> default_route.__class__
<class 'route.Route'>
[Dbg]>>> Route
<class 'route.Route'>
[Dbg]>>> type(default_route)
<class 'route.Route'>
[Dbg]>>> type(default_route) is Route
False

The class definition is really straightforward and uncomplicated:

class Route(object):
    def __init__(self, phone, condition=None):
        self.phone=phone
        self.condition=condition
        self.choice_name=None

I'm just baffled by this; why would isinstance() not return True above?

Answer 1

This could easily happen if you did the following:

1. import route and create default_route using route.Route
2. Invoke reload(route) to pull in some code changes to the module (or just for fun; doesn't matter if the module is unchanged, reload will still reload it)

You could encounter this in a similar way if default_route was also defined in route, and you did from route import Route, then reload-ed route, then did from route import default_route (order of importing Route and default_route is irrelevant, as long as a reload occurred between them, and the older one was not reimported). Either way, you have an instance and a class from subtly different versions of the module; they might look the same, have the same behaviors, etc., but they are not the same module, and therefore not the same classes, instances, etc.

In either case, a quick check would be to invoke default_route.__class__ is Route; if that evaluates to True, it's possible you've got some weird ABC based class with a broken __subclasshook__, but more likely it will evaluate to False, indicating that the two classes, despite the matching name, actually originate from independent loads of the module.