In Python 2, PyMapping_Check will return 0 for list objects. In Python 3, it returns 1. Obviously, this makes it rather difficult to differentiate between mappings and other sized iterables. In addition, it differs from the behavior of the ``collections.Mapping`` ABC -- isinstance([], collections.Mapping) returns False. I believe the new behavior is erroneous, but would like to confirm that before filing a bug. The behavior can be seen from a C extension, or if you're lazy, using ctypes: Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41) [GCC 4.3.3] on linux2 Type "help", "copyright", "credits" or "license" for more information.
import ctypes ctypes.CDLL('libpython2.6.so').PyMapping_Check(ctypes.py_object([])) 0
Python 3.0.1+ (r301:69556, Apr 15 2009, 15:59:22) [GCC 4.3.3] on linux2 Type "help", "copyright", "credits" or "license" for more information.
import ctypes ctypes.CDLL('libpython3.0.so').PyMapping_Check(ctypes.py_object([])) 1