Hi,
I'm reading the PEP 253 [1] on subtyping and there are plenty of good recommendations on how to structure the types, call tp_new and tp_init slots, etc. But, it lacks an important note on passing arguments from sub to super type. It seems the PEP is unfinished as per the note:
(XXX There should be a paragraph or two about argument passing here.)
So, I'm trying to extrapolate some strategies well known from the Python classes [2] subtyping, especially techniques that each level strips-off arguments, etc.
I'm looking for techniques to achieve similar effect to this, but in using plain Python C API (3.x):
class Shape: def __init__(self, shapename, **kwds): self.shapename = shapename super().__init__(**kwds)
class ColoredShape(Shape): def __init__(self, color, **kwds): self.color = color super().__init__(**kwds)
What would be the equivalent in C API?
Also, how to deal with similar situation but with arguments specific to derived class expected in different order, it is given at the end of the args tuple (or kwds dict, I assume principle would be same).
Here is some (pseudo-)code that illustrates the situation:
class Base: def __init__(self, x, y, z): self.x = x self.y = y self.z = z
class Derived(Base): def __init__(self, x, y, a): self.a = a super().__init__(x, y, None):
Note, if the 'a' was expected first:
Derived.__init__(self, a, x, y)
it would be similar situation to the Shape and ColoredShape above. It would be easier to deal with, I assume.
[1] http://www.python.org/dev/peps/pep-0253/ [2] http://rhettinger.wordpress.com/2011/05/26/super-considered-super/
Best regards,
Mateusz Loskot, http://mateusz.loskot.net