>>> import copy
>>> a = {"a":{"b":"con_b","c":"con_c"}}
>>> b = copy.deepcopy(a)
>>> b
{'a': {'c': 'con_c', 'b': 'con_b'}}
>>> b["a"].update({"b":"hoge"})
>>> b
{'a': {'c': 'con_c', 'b': 'hoge'}}
>>> a
{'a': {'c': 'con_c', 'b': 'con_b'}}