[Python-3000-checkins] r58240 - python/branches/py3k/Doc/library/functions.rst
skip.montanaro
python-3000-checkins at python.org
Sun Sep 23 23:13:46 CEST 2007
Author: skip.montanaro
Date: Sun Sep 23 23:13:45 2007
New Revision: 58240
Modified:
python/branches/py3k/Doc/library/functions.rst
Log:
Update the documentation of the open() builtin function a bit. I believe I
mostly got the distinction between text and binary modes correct, though
someone should proofread my writing. I also sort of guessed at the meaning
of the various index:: entries.
Modified: python/branches/py3k/Doc/library/functions.rst
==============================================================================
--- python/branches/py3k/Doc/library/functions.rst (original)
+++ python/branches/py3k/Doc/library/functions.rst Sun Sep 23 23:13:45 2007
@@ -708,19 +708,25 @@
for writing (truncating the file if it already exists), and ``'a'`` for
appending (which on *some* Unix systems means that *all* writes append to
the end of the file regardless of the current seek position). If *mode*
- is omitted, it defaults to ``'r'``.
+ is omitted, it defaults to ``'r'``. See below for more possible values
+ of *mode*.
- When opening a binary file, you should append ``'b'`` to the *mode* value
- to open the file in binary mode, which will improve portability.
- (Appending ``'b'`` is useful even on systems that don't treat binary and
- text files differently, where it serves as documentation.) See below for
- more possible values of *mode*.
+ Python distinguishes between files opened in binary and text modes, even
+ when the underlying operating system doesn't. Files opened in binary
+ mode (appending ``'b'`` to the *mode* argument to :func:``open``) return
+ contents as bytes objects without any decoding. In text mode (the
+ default, or when ``'t'`` is appended to the *mode* argument) the contents
+ of the file are returned as strings, the bytes having been first decoded
+ using the encoding specified by :func:`sys.getfilesystemencoding`.
.. index::
single: line-buffered I/O
single: unbuffered I/O
single: buffer size, I/O
single: I/O control; buffering
+ single: binary mode
+ single: text mode
+ module: sys
The optional *bufsize* argument specifies the file's desired buffer size:
0 means unbuffered, 1 means line buffered, any other positive value means
@@ -730,28 +736,20 @@
used. [#]_
Modes ``'r+'``, ``'w+'`` and ``'a+'`` open the file for updating (note
- that ``'w+'`` truncates the file). Append ``'b'`` to the mode to open
- the file in binary mode, on systems that differentiate between binary and
- text files; on systems that don't have this distinction, adding the
- ``'b'`` has no effect.
-
- In addition to the standard :cfunc:`fopen` values *mode* may be ``'U'``
- or ``'rU'``. Python is usually built with universal newline support;
- supplying ``'U'`` opens the file as a text file, but lines may be
- terminated by any of the following: the Unix end-of-line convention
- ``'\n'``, the Macintosh convention ``'\r'``, or the Windows convention
- ``'\r\n'``. All of these external representations are seen as ``'\n'`` by
- the Python program. If Python is built without universal newline support
- a *mode* with ``'U'`` is the same as normal text mode. Note that file
- objects so opened also have an attribute called :attr:`newlines` which
- has a value of ``None`` (if no newlines have yet been seen), ``'\n'``,
- ``'\r'``, ``'\r\n'``, or a tuple containing all the newline types seen.
+ that ``'w+'`` truncates the file).
- Python enforces that the mode, after stripping ``'U'``, begins with
- ``'r'``, ``'w'`` or ``'a'``.
+ When a file is opened in text mode it is also opened in universal
+ newlines mode. Unlike earlier versions of Python it's no longer
+ necessary to add a ``'U'`` value to the *mode* argument to enable this
+ mode. Consequently, in files opened in text mode lines may be terminated
+ with ``'\n'``, ``'\r'``, or ``'\r\n'``. All three external
+ representations are seen as ``'\n'`` by the Python program. File objects
+ opened in text mode also have a :attr:`newlines` attribute which has a
+ value of ``None`` (if no newlines have been seen yet), ``'\n'``,
+ ``'\r'``, ``'\r\n'``, or a tuple containing all the newline types seen.
- See also the :mod:`fileinput` module, the :mod:`os` module, and the
- :mod:`os.path` module.
+ See also the :mod:`fileinput` module, the file-related functions in the
+ :mod:`os` module, and the :mod:`os.path` module.
.. function:: ord(c)
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