The following is not the right way to iterate a MotorCursor:

for doc in cursor:
    pass

Motor should throw TypeError: MotorCursor object is not iterable. Instead, "doc" is bound to the cursor itself and the loop runs forever.

This is because, to my surprise, a Python object without an __iter__ is still iterable if it implements __getitem__. The for-loop first calls:

MotorCursor.__getitem__(0)

...which updates the delegate Cursor's skip and limit and returns the original MotorCursor. Hence the infinite loop.

It's probably best to delete __getitem__ and require you to use skip() and limit() instead; implementing __getitem__ falsely implies that a MotorCursor is iterable by conventional methods.