code: def serialize_dict_keys(d, prefix=""):
      
      keys = []
      for k, v in d.iteritems():
          fqk = '%s%s' % (prefix, k)
          keys.append(fqk)
          if isinstance(v, dict):
              keys.extend(serialize_dict_keys(v, prefix="%s." % fqk))
  
      return keys
docs: returns all the keys in a dictionary.
  
      >>> serialize_dict_keys({"a": {"b": {"c": 1, "b": 2} } })
      ['a', 'a.b', 'a.b.c', 'a.b.b']