Convert Python Class Instance to JSON

gistfile1.py

# http://stackoverflow.com/questions/1531501/json-serialization-of-google-app-engine-models
class jsonEncoder(simplejson.JSONEncoder):

  def default(self, obj):
      isa = lambda x: isinstance(obj, x) # isa(<type>)==True if obj is of type <type>
      return obj.isoformat() if isa(datetime.datetime) else \
             db.to_dict(obj) if isa(db.Model) else \
             obj.email()     if isa(users.User) else \
             simplejson.JSONEncoder.default(self, obj)