Here's a code snippet illustrating the problem.

import pymongo

class DocumentClass(dict):
pass

conn = pymongo.Connection()
db = conn['tmp']
coll = db['tmp']

obj = DocumentClass()
obj['foo'] =

coll.save(obj)

print "original object:"
print type(obj)
print type(obj['foo'])

found = coll.find_one(as_class=DocumentClass)

print
print "found object:"
print type(found)
print type(found['foo'])

The output will be:

original object:
<class '_main_.DocumentClass'>
<type 'dict'>

found object:
<class '_main_.DocumentClass'>
<class '_main_.DocumentClass'>

Note how the type of the dict-valued field changed when the object is fetched from the database with as_class. I didn't expect this behavior, and I think it's wrong.

For example, I might want to define an _init_() on my DocumentClass that adds some default fields, computes values, etc. It's incorrect to run this code for each dict-valued field.