bpo-26701: Add documentation for __trunc__ (GH-6022)
`int` fails back to `__trunc__` is `__int__` isn't defined, so cover
that in the docs.
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 3ddd280..c3b6385 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -731,8 +731,11 @@
Return an integer object constructed from a number or string *x*, or return
``0`` if no arguments are given. If *x* is a number, return
- :meth:`x.__int__() <object.__int__>`. For floating point numbers, this
- truncates towards zero.
+ :meth:`x.__int__() <object.__int__>`. If *x* defines
+ :meth:`x.__trunc__() <object.__trunc__>` but not
+ :meth:`x.__int__() <object.__int__>`, then return
+ if :meth:`x.__trunc__() <object.__trunc__>`. For floating point numbers,
+ this truncates towards zero.
If *x* is not a number or if *base* is given, then *x* must be a string,
:class:`bytes`, or :class:`bytearray` instance representing an :ref:`integer
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index 55eb41b..33aec57 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -203,7 +203,7 @@
Return the :class:`~numbers.Real` value *x* truncated to an
:class:`~numbers.Integral` (usually an integer). Delegates to
- ``x.__trunc__()``.
+ :meth:`x.__trunc__() <object.__trunc__>`.
Note that :func:`frexp` and :func:`modf` have a different call/return pattern
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 8b127a0..26ad7b8 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -2377,6 +2377,15 @@
of the appropriate type.
+.. method:: object.__trunc__(self)
+
+ Called to implement :meth:`math.trunc`. Should return the value of the
+ object truncated to a :class:`numbers.Integral` (typically an
+ :class:`int`). If a class defines :meth:`__trunc__` but not
+ :meth:`__int__`, then :meth:`__trunc__` is called to implement the
+ built-in function :func:`int`.
+
+
.. method:: object.__index__(self)
Called to implement :func:`operator.index`, and whenever Python needs to