Martin Aspeli wrote:
Hi,

I'm probably doing something very wrong, but ...

I have a general interface that can either by directly provided by an object or class (typically with implements() on the class), but could also be provided via an adapter. I have a few places where I just need to check for this (it's not really a marker interface, but I need to know whether other code later on would be able to use the interface or not).

In my tests, I tried to use queryAdapter(), but that didn't return anything when the interface was implemented directly by the class. Similarly, Interface.providedBy() returns (expectedly) False if the interface could only be obtained via an adapter. Currently I do:

      try:
            adapted = IFoo(context)
            return True
        except (ComponentLookupError, TypeError):
            return False

but that's just silly... Is there a pattern for this?

adapted = IFoo(conext, None):
if adapted is not None:
  ...

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