python之如何在 App Engine 中从 JSON 中排除 db.Blob

我正在使用 question 2114659 中引用的 jsonGQL 版本和 available in the svn对于 eve-pos-tracker。

我和这个可怜的应用引擎开发者有同样的问题: https://groups.google.com/group/google-appengine/browse_thread/thread/f7a44b707119013c/81ba15c883ba95fe

我的 json 序列化在我的模型中遇到 png 图像 (0x89) 的二进制数据时崩溃。我不需要序列化此数据，所以我想跳过该字段或简单地输出类似 <binary> 的内容.

这是处理程序:

class FillList(webapp.RequestHandler): 
    def get(self): 
        fills = Fill.all() 
        self.response.headers['Content-Type'] = 'application/json' 
        self.response.out.write(jsonGQL.encode(fills.fetch(100))) 

我试过这个:

  elif isinstance(obj, db.Blob): 
      return "<binary>" 

但错误依然存在。回溯是:

    Traceback (most recent call last): 
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/webapp/_webapp25.py", line 701, in __call__ 
    handler.get(*groups) 
  File "~/app/api.py", line 61, in get 
    self.response.out.write(jsonGQL.encode(fills.fetch(100))) 
  File "~/app/jsonGQL.py", line 103, in encode 
    return GqlEncoder().encode(input, exclude=[]) 
  File "~/app/jsonGQL.py", line 87, in encode 
    return simplejson.JSONEncoder.encode(self, o) 
  File "~/app/simplejson/encoder.py", line 216, in encode 
    chunks = list(chunks) 
  File "~/app/simplejson/encoder.py", line 482, in _iterencode 
    for chunk in _iterencode_list(o, _current_indent_level): 
  File "~/app/simplejson/encoder.py", line 380, in _iterencode_list 
    for chunk in chunks: 
  File "~/app/simplejson/encoder.py", line 496, in _iterencode 
    for chunk in _iterencode(o, _current_indent_level): 
  File "~/app/simplejson/encoder.py", line 485, in _iterencode 
    for chunk in _iterencode_dict(o, _current_indent_level): 
  File "~/app/simplejson/encoder.py", line 439, in _iterencode_dict 
    yield _encoder(value) 
  File "~/app/simplejson/encoder.py", line 50, in py_encode_basestring_ascii 
    s = s.decode('utf-8') 
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/encodings/utf_8.py", line 16, in decode 
    return codecs.utf_8_decode(input, errors, True) 
UnicodeDecodeError: 'utf8' codec can't decode byte 0x89 in position 0: invalid start byte 

请您参考如下方法:

这是我的解决方案

    elif isinstance(obj, db.Model): 
        properties = obj.properties().items() 
        output = {} 
        for field, value in properties: 
            data =  getattr(obj, field) 
            if isinstance(data, str): 
                # db.Blob inherits from str 
                data = data.encode('string-escape') 
            output[field] = data 
        output['id'] = obj.key().id() 
        return output