Python object traversing

ot.py

#!/usr/bin/env python3
# Copyright (c) 2012 Yu-Jie Lin
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy of
# this software and associated documentation files (the "Software"), to deal in
# the Software without restriction, including without limitation the rights to
# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
# of the Software, and to permit persons to whom the Software is furnished to do
# so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

import re


def ot_attr(obj, key):

  if hasattr(obj, key):
    return getattr(obj, key)
  raise KeyError


def ot_item(obj, key):

  try:
    return obj.__getitem__(key)
  except:
    raise KeyError


def ot_index_item(obj, key):
  '''For list or string or something'''
  try:
    return obj.__getitem__(int(key))
  except:
    raise KeyError


def ot(obj, path, key_funcs=None):
  '''ot stands for object traversing'''
  if key_funcs is None:
    key_funcs = (ot_attr, ot_item, ot_index_item)

  keys = re.split(r'(?<!\\)\.', path)
  key_idx = 0
  while key_idx < len(keys):
    key = keys[key_idx].replace(r'\.', '.')
    key_idx += 1

    for f in key_funcs:
      try:
        obj = f(obj, key)
        break
      except KeyError:
        continue
    else:
      raise KeyError(('No key %s in object.%s' % (key, '.'.join(keys[:key_idx-1]))).rstrip('. '))
  return obj


if __name__ == '__main__':

  class ThisCanNotBeFound:
    pass

  test_dict = {'number': 123,
               'boolean': True,
               'tuple': (1, 2, 3),
               ThisCanNotBeFound: 'Oh no!',
               }
  test_dict['list'] = ['number',
                       456,
                       {'foo.bar': 'It is foobar!'},
                       ]

  print(ot(test_dict, 'number'))
  print(ot(test_dict, 'boolean'))
  print(ot(test_dict, 'tuple.1'))
  print(ot(test_dict, 'tuple.__repr__')())
  print(ot(test_dict, 'list'))
  print(ot(test_dict, 'list.2.foo\\.bar'))
  print(ot(test_dict, 'list.2.foo\\.bar.4'))
  print(ot('string', '2'))