Albert-Jan Roskam wrote:
> I have two classes with a number of methods that are the same, so I want
to define a super class that holds these methods. But the super class (below
called _Generic) should not be instantiated, because it serves no purpose
other than the DRY principle. I raise a NotImplementedError in case if
somebody dares to instantiate _Generic. Below, only one common method is
defined in_Generic, namely __repr__ (the other ones are __enter__ and
__exit__, maybe more, if you must know). At first I thought I'd need the abc
module for this, but this seems to do the trick. I do not want to enforce
concrete implementations of abstract methods, which is the goal of abc. Is
this the way to do this, or this this quirky code?
I think this is OK, but I don't understand your argument against
# python 2
class _Generic:
__metaclass__ = abc.ABCMeta
@abc.abstractmethod
def __init__(self, *args, **kwargs):
pass
either.
> import inspect
>
> class _Generic(object):
>
> def __init__(self, *args, **kwargs):
> raise NotImplementedError
>
> def __repr__(self):
> fmt = []
> for arg in inspect.getargspec(self.__init__).args[1:]:
> value = getattr(self, arg)
> sr = "%r" if isinstance(value, basestring) else "%s"
> fmt.append(("%s=" + sr) % (arg, value))
> return self.__class__.__name__ + "(" + ", ".join(fmt) + ")"
>
> class Concrete(Generic):
>
> def __init__(self, x=42, y='a'):
> self.x = x
> self.y = y
>
> class OneMore(Generic):
>
> def __init__(self, w=555, z='foo'):
> self.w = w
> self.z = z
>
>
> c = Concrete()
> print repr(c)
>
> a = _Generic(666) # NotImplementedError
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