How to verify if class implements a rich comparison method?

With the old style classes simply using hasattr works:

>>> class old:
...     pass
...
>>> hasattr(old, '__eq__')
False

Using the new style classes every class has the attribute __eq__:

>>> class nsc(object):
...     pass
...
>>> hasattr(nsc, '__eq__')
True

This is the expected behaviour as hasattr(object, '__eq__') also returns True. This is true for every rich comparison method.

How to verify if class implements a rich comparison method if I can't use hasattr? One thing that comes to mind is to call the method and see if it raises a NotImplemented exception. But calling those methods may have unexpected damages.

You can do it by using dir instead of hasattr. Rich comparison methods don't appear in the list returned by the dir function.

>>> class nsc(object):
...     pass
...
>>> '__eq__' in dir(nsc)
False