mongodb/mongo-python-driver — pull request #238 by dmitchell (2014-06-04 19:40:45+00:00)
Title: Don't unnecessarily copy the key list

`__iter__, has_key, __contains__, clear, & len` all copy the `__keys` list but don't need to.

Minor backward compatibility change: make `__iter__` generate a runtime error if the user attempts to destructively modify the `SON` during iteration just as `dict` does and have the others directly use the internal list.