A call to ``format(value, format_spec)`` is translated to
``type(value).__format__(format_spec)`` which bypasses the instance
dictionary when searching for the value's :meth:`__format__` method. A
- :exc:`TypeError` exception is raised if the method is not found or if either
- the *format_spec* or the return value are not strings.
+ :exc:`TypeError` exception is raised if the method search reaches
+ :mod:`object` and the *format_spec* is non-empty, or if either the
+ *format_spec* or the return value are not strings.
- .. versionadded:: 3.4
+ .. versionchanged:: 3.4
``object().__format__(format_spec)`` raises :exc:`TypeError`
- if *format_spec* is not empty string.
+ if *format_spec* is not an empty string.
.. _func-frozenset:
The return value must be a string object.
+ .. versionchanged:: 3.4
+ The __format__ method of ``object`` itself raises a :exc:`TypeError`
+ if passed any non-empty string.
+
.. _richcmpfuncs:
.. method:: object.__lt__(self, other)
* :class:`inspect.Signature`: positional-only parameters are now required
to have a valid name.
+* :meth:`object.__format__` no longer accepts non-empty format strings, it now
+ raises a :exc:`TypeError` instead. Using a non-empty string has been
+ deprecated since Python 3.2. This change has been made to prevent a
+ situation where previously working (but incorrect) code would start failing
+ if an object gained a __format__ method, which means that your code may now
+ raise a :exc:`TypeError` if you are using an ``'s'`` format code with objects
+ that do not have a __format__ method that handles it. See :issue:`7994` for
+ background.
+
Code Cleanups
-------------