$ python  0222_ordereddict.py 
<class 'dict'>
c 3
dict_items([('b', 1), ('a', 2)])
<class 'collections.OrderedDict'>
b 1
odict_items([('a', 2), ('c', 3)])
<class 'collections.OrderedDict'>
c 3
odict_items([('b', 1), ('a', 2)])