Recursive Generator Error?

[David]

I have a tree-like data structure, the basic elements are hash tables,
and they are grouped into lists, like [[{'a':1},[{'b':2}]]].
And I want to flat the lists and visit hash table one by one, like {'a':1}, {'b':2}.
But my program didn't work as I wish. When it entered the 2nd
flat_yield, it threw a GeneratorExit. Is there anything wrong?
Thank you very much!

#- - - - - - - - - - 
def flat_yield(tbl_list):
    for t in tbl_list:
        if type(t) == type({}):
            yield t
        elif type(t) == type([]):
            flat_yield(t)
a = [[{'a':1},[{'b':2}]]]
for i in flat_yield(a):
    print i