can i implement virtual functions in python ?

[Andrew Dalke]

logistix at cathoderaymission.net:
> if you want to create a genuine Abstract Base Class, raise
> NotImplementedErrors for the virual methods.  People will tell you
> that this is not 'pythonic' (you should be using hasattr() to test for
> interfaces) but I still find it useful from time to time.

Really?  I find hasattr to be non-Pythonic.  Just get the object, like

  try:
    method = obj.function_name
  except AttributeError:
    ... not implemented ...

However, I do use NotImplementedError so the exception
which percolates up is more obvious than AttributeError.  It also
allows me to put in a docstring describing the interface requirements
of derived classes.

I also don't like the double attribute lookup in

  if not hasattr(obj, "function_name"):
    ... not implemented ...
  else:
    obj.function_name(...)

but that's more a personal issue than Pythonic vs. non-Pythonic.

                    Andrew
                    dalke at dalkescientific.com