[PyCrust] Attribute list hook

[Neil H. <nho...@bi...>]

   On the PythonCard list I've been pushing the use of __getattr__ and
__setattr__ to allow access to widget properties through dot notation -

    self.components.btnTranslate.label = "Celsius to Fahrenheit"

 rather than

    self.components.getWidget("btnTranslate").setLabel("Celsius to
Fahrenheit")

   One problem with this is that interactive shells such as PyCrust can't
find out the names of these attributes as they are not in __dict__ even
though the set of such attributes is normally well known. This is easy
enough to solve in the context of PythonCard using PyCrust by adding some
code (or stuffing __dict__ with the known attributes) but this is a generic
problem that should be solved for use by all interactive shells.

   Has this been solved for any other shells?

   If not, I propose a convention which is to provide a getAttributeNames
method on any class that wants to expose its dynamic (or semi-dynamic)
attributes to shells. Thus

class D11:
    def getAttributeNames(self):
        return ["woderwick", "woger", "weginald"]

class D12:
    pass

def attrList(d):
    try:
        print d.getAttributeNames()
    except AttributeError, x:
        print "Empty"

Then interactively:

>>> d = D11()
>>> attrList(d)
['woderwick', 'woger', 'weginald']
>>> e = D12()
>>> attrList(e)
Empty

   If there is resistance to using exceptions here, then a more complex
mechanism that involves checking the __class__ and __class__.__bases__ could
be used or a marker attribute added.

   I'll leave this message here for a day and if there are no big problems
will copy it to comp.lang.python to see if there are more opinions.

   Neil