another iteration on the path-like dictionary access. This makes it into a class and uses getters and setters, a much more elegant solution

pathlike_dict_access_class.py

import sys, json
#inspired by http://stackoverflow.com/questions/14692690/access-python-nested-dictionary-items-via-a-list-of-keys

# Testing dictionary
D = {
  "a": {
    "aa": {
      "aaa": 1,
      "aab": 2
    },
    "ab": {
      "aba": 3,
      "abb": 4
    }
  },
  "b": {
    "ba": 5,
    "bb": 6
  },
  "c": 7
}

# Some example paths
P1 = "a:aa:aaa" # 1
P2 = "a:aa:aab" # 2
P3 = "a:ab:aba" # 3
P4 = "a:ab" # {"aba": 3, "abb": 4}
P5 = "b:ba" # 5
P6 = "c" # 7
P7 = "a:ba:aba" # err

##Hardcoded delimiter##
# class path_lookup(object):
#     def __init__(self, data):
#         self.data = data
#     def __getitem__(self, path):
#         if path == "":
#             return self.data
#         else:
#             path_list = path.split(":")
#             try:
#               return reduce(lambda d, k: d[k], path_list, self.data)
#             except KeyError:
#               print("[path_lookup] Innapropriate path: " + path)
#     def __setitem__(self, path, value):
#           if ":" not in path:
#             self.data[path] = value
#           else:
#             path_list = path.rsplit(":",1)
#             try:
#               self.data[path_list[0]][path_list[1]] = value
#             except KeyError:
#               print "[path_set] Innapropriate destination path: " + path_list[0]

##this version takes lists!##
class path_lookup(object):
    def __init__(self, data):
        self.data = data
    def __getitem__(self, path):
        if path == []:
            return self.data
        else:
            try:
              return reduce(lambda d, k: d[k], path, self.data)
            except KeyError:
              print("[path_get] Innapropriate path: " + str(path))
    def __setitem__(self, path, value):
          print path
          if len(path) == 1:
            self.data[path] = value
          else:
            try:
              reduce(lambda d, k: d[k], path[:-1], self.data)[path[-1]] = value
            except KeyError:
              print "[path_set] Innapropriate destination path: " + path

def main():
  d = path_lookup(D)
  print d[P1.split(":")]
  print d[P2.split(":")]
  print d[P3.split(":")]
  print d[P4.split(":")]
  print d[P5.split(":")]
  print d[P6.split(":")]
  print d[P7.split(":")]
  d["a:here".split(":")] = 11
  print d["a:here".split(":")]

if __name__=="__main__":
  main()