def _merge_a_into_b(a, b):
  """Merge config dictionary a into config dictionary b, clobbering the
  options in b whenever they are also specified in a.
  """
  if type(a) is not edict:
    return

  for k, v in a.items():
    # a must specify keys that are in b
    if k not in b:
      raise KeyError('{} is not a valid config key'.format(k))

    # the types must match, too
    old_type = type(b[k])
    if old_type is not type(v):
      if isinstance(b[k], np.ndarray):
        v = np.array(v, dtype=b[k].dtype)
      else:
        raise ValueError(('Type mismatch ({} vs. {}) '
                          'for config key: {}').format(type(b[k]),
                                                       type(v), k))

    # recursively merge dicts
    if type(v) is edict:
      try:
        _merge_a_into_b(a[k], b[k])
      except:
        print(('Error under config key: {}'.format(k)))
        raise
    else:
      b[k] = v
Merge config dictionary a into config dictionary b, clobbering the
  options in b whenever they are also specified in a.
  
lib/model/utils/config.py