from json import JSONEncoder
  def _default(self, obj):
    return getattr(obj.__class__, "to_json", _default.default)(obj)
  _default.default = JSONEncoder().default
  default.JSONEncoder.default = _default

class Tmp:
  def __init__(self, id, name):
    self.id = id
    self.name = name

  def to_json():
    # 返回自定义对象json串
    pass

 def _iterencode(o, _current_indent_level):
    if isinstance(o, basestring):
      yield _encoder(o)
    elif o is None:
      yield 'null'
    elif o is True:
      yield 'true'
    elif o is False:
      yield 'false'
    elif isinstance(o, (int, long)):
      yield str(o)
    elif isinstance(o, float):
      yield _floatstr(o)
    elif isinstance(o, (list, tuple)):
      for chunk in _iterencode_list(o, _current_indent_level):
        yield chunk
    elif isinstance(o, dict):
      for chunk in _iterencode_dict(o, _current_indent_level):
        yield chunk
    else:
      if markers is not None:
        markerid = id(o)
        if markerid in markers:
          raise ValueError("Circular reference detected")
        markers[markerid] = o
      o = _default(o)
      for chunk in _iterencode(o, _current_indent_level):
        yield chunk
      if markers is not None:
        del markers[markerid]

r'''
Specializing JSON object decoding::

  > import json
  > def as_complex(dct):
  ...   if '__complex__' in dct:
  ...     return complex(dct['real'], dct['imag'])
  ...   return dct
  ...
  > json.loads('{"__complex__": true, "real": 1, "imag": 2}',
  ...   object_hook=as_complex)
  (1+2j)
  > from decimal import Decimal
  > json.loads('1.1', parse_float=Decimal) == Decimal('1.1')
  True

Specializing JSON object encoding::

  > import json
  > def encode_complex(obj):
  ...   if isinstance(obj, complex):
  ...     return [obj.real, obj.imag]
  ...   raise TypeError(repr(o) + " is not JSON serializable")
  ...
  > json.dumps(2 + 1j, default=encode_complex)
  '[2.0, 1.0]'
  > json.JSONEncoder(default=encode_complex).encode(2 + 1j)
  '[2.0, 1.0]'
  > ''.join(json.JSONEncoder(default=encode_complex).iterencode(2 + 1j))
  '[2.0, 1.0]'
'''