for in sequence problem... possible new operator to add to python

[Adam Gent]

I was fooling around subclassing a dictionary object and noticed that
when
I do the standard "for in <object-is-a-sequence>:" that I have no
control on how python gets that sequence.

For example:

class Blah(dict):
   pass

bl = Blah()

for b in bl:
    #b will be a key and not a value
    #no matter how I subclass Blah

However I want b to be the values with out doing:
for b in bl.values()

I could be wrong on this but I believe python is missing an operator
for looping over objects. I think there should be a __sequence__ or
__forsequence__ operator that returns a sequence when "for x in
object" syntax is used.
So
for b in bl: == for b in bl.__sequence__