Using metaclasses to inherit class variables

[telesphore4 at gmail.com]

Hmm. setattr() only does a shallow search. Good to know.

Your

    if not name in dict: setattr(cls, name, value)

is a more succinct/better way of writing

    if not cls.__dict__.has_key(var): setattr(cls, var, val)

Which i tested a fair bit.

OK it appears that both are working for the simple types. However, if I
do:

>>> class SetClassVars(type):
...     cvars = dict(lst=[], desc=None)
...     def __init__(cls, name, bases, classdict):
...         for name, value in SetClassVars.cvars.iteritems():
...              if not name in classdict: setattr(cls, name, value)

>>> class C(object):
...      __metaclass__ = SetClassVars
...      desc = 'foo'
...
>>> class D(C):
...     desc = bar

>>> C.lst.append('ccccc')
>>> D.lst.append('dddd')
>>> C.lst
['ccccc', 'dddd']
>>> D.lst
['ccccc', 'dddd']

I get the piling on behavior.

OK. So it seems to be a problem only with the mutable list. I made the
mistake of thinking that the list behavior was the same as for
non-mutables.

This must be a newbie mistake and it is probably documented somewhere.
*Ding* I'll bet it is the same one that bites newbies when they define
functions like:

def myfunc(lst=[]):

Looking for complicated problems with metaclasses when simple mistakes
about mutables are the issue. Occam wags his finger at me.

Thank you. That helped.
t4