Improve str() and object.__str__() documentation (issue #13538).
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index f9e0d0a..0d8f61c 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -528,7 +528,7 @@
is used by most built-in types: :ref:`formatspec`.
The default *format_spec* is an empty string which usually gives the same
- effect as calling ``str(value)``.
+ effect as calling :func:`str(value) <str>`.
A call to ``format(value, format_spec)`` is translated to
``type(value).__format__(format_spec)`` which bypasses the instance
@@ -1246,38 +1246,51 @@
For more information on static methods, consult the documentation on the
standard type hierarchy in :ref:`types`.
+ .. index::
+ single: string; str() (built-in function)
+
.. function:: str(object='')
- str(object[, encoding[, errors]])
+ str(object=b'', encoding='utf-8', errors='strict')
- Return a string version of an object, using one of the following modes:
+ Return a :ref:`string <typesseq>` version of *object*. If *object* is not
+ provided, returns the empty string. Otherwise, the behavior of ``str()``
+ depends on whether *encoding* or *errors* is given, as follows.
- If *encoding* and/or *errors* are given, :func:`str` will decode the
- *object* which can either be a byte string or a character buffer using
- the codec for *encoding*. The *encoding* parameter is a string giving
- the name of an encoding; if the encoding is not known, :exc:`LookupError`
- is raised. Error handling is done according to *errors*; this specifies the
- treatment of characters which are invalid in the input encoding. If
- *errors* is ``'strict'`` (the default), a :exc:`ValueError` is raised on
- errors, while a value of ``'ignore'`` causes errors to be silently ignored,
- and a value of ``'replace'`` causes the official Unicode replacement character,
- U+FFFD, to be used to replace input characters which cannot be decoded.
- See also the :mod:`codecs` module.
+ If neither *encoding* nor *errors* is given, ``str(object)`` returns
+ :meth:`object.__str__() <object.__str__>`, which is the "informal" or nicely
+ printable string representation of *object*. For string objects, this is
+ the string itself. If *object* does not have a :meth:`~object.__str__`
+ method, then :func:`str` falls back to returning
+ :meth:`repr(object) <repr>`.
- When only *object* is given, this returns its nicely printable representation.
- For strings, this is the string itself. The difference with ``repr(object)``
- is that ``str(object)`` does not always attempt to return a string that is
- acceptable to :func:`eval`; its goal is to return a printable string.
- With no arguments, this returns the empty string.
+ .. index::
+ single: buffer protocol; str() (built-in function)
+ single: bytes; str() (built-in function)
- Objects can specify what ``str(object)`` returns by defining a :meth:`__str__`
- special method.
+ If at least one of *encoding* or *errors* is given, *object* should be a
+ :class:`bytes` or :class:`bytearray` object, or more generally any object
+ that supports the :ref:`buffer protocol <bufferobjects>`. In this case, if
+ *object* is a :class:`bytes` (or :class:`bytearray`) object, then
+ ``str(bytes, encoding, errors)`` is equivalent to
+ :meth:`bytes.decode(encoding, errors) <bytes.decode>`. Otherwise, the bytes
+ object underlying the buffer object is obtained before calling
+ :meth:`bytes.decode`. See the :ref:`typesseq` section, the
+ :ref:`typememoryview` section, and :ref:`bufferobjects` for information on
+ buffer objects.
- For more information on strings see :ref:`typesseq` which describes sequence
- functionality (strings are sequences), and also the string-specific methods
- described in the :ref:`string-methods` section. To output formatted strings,
- see the :ref:`string-formatting` section. In addition see the
- :ref:`stringservices` section.
+ Passing a :class:`bytes` object to :func:`str` without the *encoding*
+ or *errors* arguments falls under the first case of returning the informal
+ string representation (see also the :option:`-b` command-line option to
+ Python). For example::
+
+ >>> str(b'Zoot!')
+ "b'Zoot!'"
+
+ ``str`` is a built-in :term:`type`. For more information on the string
+ type and its methods, see the :ref:`typesseq` and :ref:`string-methods`
+ sections. To output formatted strings, see the :ref:`string-formatting`
+ section. In addition, see the :ref:`stringservices` section.
.. function:: sum(iterable[, start])