Checking for usual descriptors in Python 2.3

[=?iso-8859-1?Q?Fran=E7ois?= Pinard]

This question is a bit technical, but hopefully, this list will offer me
good hints or nice solutions. Happily enough for me, it often does!

I would need to recognise and play with descriptor types, like:

member descriptors
method descriptors
getset descriptors
wrapper descriptors

but do not find how to easily refer to them, either from existing
constructor types (like we could do with `property', say), nor from
members of the `types' module. I also wonder how much I can "get into"
these various descriptors or tear them apart...


P.S. - If you are curious, my real goal is creating some metaclass able
to build kind-of-shadow classes for various pygtk widgets, lazily, on
the fly. If experimentation shows that this is not speedy enough, than
I may rather have a pre-processor that would produce Python source
instead. In any case, I need to learn how to explore descriptors at run
time, rather than working hard at scanning/parsing real pygtk sources.

 

[Michael Hudson]

This question is a bit technical, but hopefully, this list will offer me
good hints or nice solutions. Happily enough for me, it often does!

I would need to recognise and play with descriptor types, like:

member descriptors
method descriptors
getset descriptors
wrapper descriptors

but do not find how to easily refer to them, either from existing
constructor types (like we could do with `property', say), nor from
members of the `types' module. I also wonder how much I can "get into"
these various descriptors or tear them apart...

If you want to know whether 'ob' is a descriptor,

hasattr(ob, '__get__')

is pretty close. PEP 252 is also your friend.

P.S. - If you are curious, my real goal is creating some metaclass
able to build kind-of-shadow classes for various pygtk widgets,
lazily, on the fly.

I'm not sure how this reletes to the above, but have fun

You may find it sensible to just restrict yourself to a finite set of
descriptors you know how to deal with.

Cheers,
mwh

 

[Michael Hudson]

If you want to know whether 'ob' is a descriptor,

hasattr(ob, '__get__')

is pretty close. PEP 252 is also your friend.

On the off chance that this wasn't what you were asking -) and you
wanted to get your hands on the type objects of each of the given
descriptor types, the only way I can think of doing that is getting
your hands on one and calling type() on it.

member: type(type.__dict__['__dictoffset__'])
method: type(list.append)
getset: type(object.__dict__['__class__'])
wrapper: type(object.__dict__['__getattribute__'])

As to how introspectable each of these are, the interactive
interpreter (or the source) is now your friend.

HTH,
mwh