django 错误：ValueError: Circular reference detected，具体错误信息：
File "C:\Python27\MyDjango\jianzhi_002\jianzhi_app\views.py", line 418, in wx_get_job_detail
return HttpResponse(json.dumps({'message': message, 'data': detail_data}))
File "C:\Python27\lib\json\__init__.py", line 244, in dumps
return _default_encoder.encode(obj)
File "C:\Python27\lib\json\encoder.py", line 207, in encode
chunks = self.iterencode(o, _one_shot=True)
File "C:\Python27\lib\json\encoder.py", line 270, in iterencode
return _iterencode(o, 0)
ValueError: Circular reference detected
错误意思：存在循环引用。
代码重现：
import json
a = b = c = {}
# 将b c 存到 a
a['b'] = b
a['c'] = c
json.dumps(a)
ValueError Traceback (most recent call last) <ipython-input-5-2f50cf32d976> in <module>() ----> 1 json.dumps(a) /usr/lib/python2.7/json/__init__.pyc in dumps(obj, skipkeys, ensure_ascii, check_circular, allow_nan, cls, indent, separators, encoding, default, sort_keys, **kw) 241 cls is None and indent is None and separators is None and 242 encoding == 'utf-8' and default is None and not sort_keys and not kw): --> 243 return _default_encoder.encode(obj) 244 if cls is None: 245 cls = JSONEncoder /usr/lib/python2.7/json/encoder.pyc in encode(self, o) 205 # exceptions aren't as detailed. The list call should be roughly 206 # equivalent to the PySequence_Fast that ''.join() would do. --> 207 chunks = self.iterencode(o, _one_shot=True) 208 if not isinstance(chunks, (list, tuple)): 209 chunks = list(chunks) /usr/lib/python2.7/json/encoder.pyc in iterencode(self, o, _one_shot) 268 self.key_separator, self.item_separator, self.sort_keys, 269 self.skipkeys, _one_shot) --> 270 return _iterencode(o, 0) 271 272 def _make_iterencode(markers, _default, _encoder, _indent, _floatstr,ValueError: Circular reference detected
究其原因，是因为 a b c 实际上指向的是同一个对象的引用。
解决办法：
import json
a, b , c = {}, {}, {}
# 将b c 存到 a
a['b'] = b
a['c'] = c
json.dumps(a)
总结：
一般遇到ValueError: Circular reference detected错误，是因为同一个变量被循环引用导致的bug。检查代码中哪一个变量被循环引用，更改变量名就可以。
