type and vice versa. For builtin types, a dictionary will be returned that
cannot be changed (but still looks and behaves like a normal dictionary).
+* the ``__len__`` or ``__length_hint__`` special methods are sometimes
+ called by CPython to get a length estimate to preallocate internal arrays.
+ So far, PyPy never calls ``__len__`` for this purpose, and never calls
+ ``__length_hint__`` at all.