trunc does use the special method, though

benjaminp · benjaminp · commit 09203c14b237 · 2010-07-01T23:35:37.000Z
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
@@ -134,7 +134,7 @@ Number-theoretic and representation functions
 .. function:: trunc(x)
 
    Return the :class:`Real` value *x* truncated to an :class:`Integral` (usually
-   a long integer).
+   a long integer).  Uses the ``__trunc__`` method.
 
    .. versionadded:: 2.6
 
