Printing a dictionary of class instances

[Alex Martelli]

Grant Ito wrote:

> I have created a dictionary where the values are instances of a class. I'm
> wondering if it's possible to use the format operator (%) to access an
> instance member variable.
> 
> sample:
>>>> dict1 = {'a' : 1}
>>>> print "%(a)s" % (dict1)
> 1
>>>> class testclass(object):
> ...  def __init__(self):
> ...   self.var1 = 1
> ...   return
> ...
>>>> oneInstance = testclass()
>>>> testdict = {}
>>>> testdict['a'] = oneInstance
>>>> testdict['a'].var1
> 1
>>>> print "%(a.var1)s" % (testdict)
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> KeyError: a.var1
> 
> Is there any way to write that last "print" line to make this work?

Only by using as testdict, not a dictionary, but a smart mapping
that knows how you want to use dots as separators.  E.g.  for just
one level of dots:


class dotdict(dict):

    def __getitem__(self, key):
        realkey, attrname = key.split('.', 1)
        obj = dict.__getitem__(self, realkey)
        return getattr(obj, attrname)

testdict = dotdict({'a': oneInstance})


Alex