Logged In: YES 
user_id=4771

This is a known documentation bug: all this is expected, but
under-documented.  Indeed, len(x) calls the special method
__len__ of 'x', but what is not specified is the real
definition of "calling a special method" on an object 'x':
it is to look up the name "__len__" in the dict of type(x),
then in the dict of the parent types in MRO order.  It's
really not the same thing as an attribute lookup.