#2530: io module documentation.

1 files changed, 603 insertions, 0 deletions

diff --git a/Doc/library/io.rst b/Doc/library/io.rst
new file mode 100644
index 0000000..ec0d51e
--- /dev/null
+++ b/Doc/library/io.rst
@@ -0,0 +1,603 @@
+:mod:`io` --- Core tools for working with streams
+=================================================
+
+.. module:: io
+   :synopsis: Core tools for working with streams.
+.. moduleauthor:: Guido van Rossum <guido@python.org>
+.. moduleauthor:: Mike Verdone <mike.verdone@gmail.com>
+.. moduleauthor:: Mark Russell <mark.russell@zen.co.uk>
+.. sectionauthor:: Benjamin Peterson
+
+The :mod:`io` module provides the Python interfaces to stream handling.  The
+builtin :func:`open` function is defined in this module.
+
+At the top of the I/O hierarchy is the abstract base class :class:`IOBase`.  It
+defines the basic interface to a stream.  Note, however, that there is no
+seperation between reading and writing to streams; implementations are allowed
+to throw an :exc:`IOError` if they do not support a given operation.
+
+Extending :class:`IOBase` is :class:`RawIOBase` which deals simply with the
+reading and writing of raw bytes to a stream.  :class:`FileIO` subclasses
+:class:`RawIOBase` to provide an interface to OS files.
+
+:class:`BufferedIOBase` deals with buffering on a raw byte stream
+(:class:`RawIOBase`).  Its subclasses, :class:`BufferedWriter`,
+:class:`BufferedReader`, and :class:`BufferedRWPair` buffer streams that are
+readable, writable, and both respectively.  :class:`BufferedRandom` provides a
+buffered interface to random access streams.  :class:`BytesIO` is a simple
+stream of in-memory bytes.
+
+Another :class:`IOBase` subclass, :class:`TextIOBase` deals with the encoding
+and decoding of streams into text.  :class:`TextIOWrapper`, which extends it, is
+a buffered text interface to a buffered raw stream (:class:`BufferedIOBase`).
+Finally, :class:`StringIO` is a in-memory stream for text.
+
+
+Module Interface
+----------------
+
+.. data:: DEFAULT_BUFFER_SIZE
+
+   An int containing the default buffer size used by the module's buffered I/O
+   classes.  :func:`open` uses the file's blksize (as obtained by os.stat) if
+   possible.
+
+.. function:: open(file[, mode[, buffering[, encoding[, errors[, newline[, closefd=True]]]]]])
+
+   Open *file* and return a stream.
+
+   *file* is a string giving the name of the file, or an integer file descriptor
+   of the file to be wrapped.
+
+   The optional *mode* string determines how the file is opened and consists of
+   a combination of the following characters:
+
+   ========= ===============================================================
+   Character Meaning
+   --------- ---------------------------------------------------------------
+   ``'r'``   open for reading (default)
+   ``'w'``   open for writing, truncating the file first
+   ``'a'``   open for writing, appending to the end of the file if it exists
+   ``'b'``   binary mode
+   ``'t'``   text mode (default)
+   ``'+'``   open a disk file for updating (reading and writing)
+   ``'U'``   universal newline mode (for backwards compatibility; unneeded
+             for new code)
+   ========= ===============================================================
+
+   The default mode is ``'rt'`` (open for reading text).  For binary random
+   access, the mode ``'w+b'`` opens and truncates the file to 0 bytes, while
+   ``'r+b'`` opens the file without truncation.
+
+   *buffering* is an optional argument controling the buffering of the returned
+   stream.  A value of ``0`` means no buffering, ``1`` means line buffered, and
+   a greater value means full buffering with the given buffer size.  Buffering
+   cannot be disabled in text mode.
+
+   *encoding* is the name of the encoding used to decode or encode the file.
+   This may only be used in text mode.  Any encoding available in the
+   :mod:`codecs` module registry can be used.
+
+   *errors* specifies how the encoding should treat errors.  "strict", the
+   default raises a :exc:`ValueError` on problems.  See the *errors* argument
+   of :func:`codecs.open` for more information. XXX
+
+   *newline* controls how universal newlines works (it only applies to text
+   mode).  It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``.  It
+   works as follows:
+
+   * On input, if *newline* is ``None``, universal newlines mode is enabled.
+     Lines in the input can end in ``'\n'``, ``'\r'``, or ``'\r\n'``, and these
+     are translated into ``'\n'`` before being returned to the caller.  If it is
+     ``''``, universal newline mode is enabled, but line endings are returned to
+     the caller untranslated.  If it has any of the other legal values, input
+     lines are only terminated by the given string, and the line ending is
+     returned to the caller untranslated.
+
+   * On output, if *newline* is ``None``, any ``'\n'`` characters written are
+     translated to the system default line separator, :data:`os.linesep`.  If
+     *newline* is ``''``, no translation takes place.  If *newline* is any of
+     the other legal values, any ``'\n'`` characters written are translated to
+     the given string.
+
+   If *closefd* is :keyword:`False`, the underlying file descriptor will be kept
+   open when the file is closed.  This does not work when a file name is given.
+
+   The :func:`open` function returns a file object whose type depends on the
+   mode, and through which the standard file operations such as reading and
+   writing are performed.  When :func:`open` is used to open a file in a text
+   mode (``'w'``, ``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a
+   :class:`TextIOWrapper`.  When used to open a file in a binary mode, the
+   returned class varies: in read binary mode, it returns a
+   :class:`BufferedReader`; in write binary and append binary modes, it returns
+   a :class:`BufferedWriter`, and in read/write mode, it returns a
+   :class:`BufferedRandom`.
+
+   It is also possible to use a string or bytearray as a file for both reading
+   and writing.  For strings :class:`io.StringIO` can be used like a file opened
+   in a text mode, and for bytes a :class:`io.BytesIO` can be used like a file
+   opened in a binary mode.
+
+
+.. exception:: BlockingIOError
+
+   Error raised when blocking would occur on a non-blocking stream.  It inherits
+   :exc:`IOError`.
+
+   In addition to those of :exc:`IOError`, :exc:`BlockingIOError` has one
+   attribute:
+
+   .. attribute:: characters_written
+
+      An integer containing the number of characters written to the stream
+      before it blocked.
+
+
+.. exception:: UnsupportedOperation
+
+   An exception inheriting :exc:`IOError` and :exc:`ValueError` that is raised
+   when an unsupported operation is called on a stream.
+
+
+I/O Base Classes
+----------------
+
+.. class:: IOBase
+
+   The abstract base class for all I/O classes, acting on streams of bytes.
+   There is no public constructor.
+
+   This class provides dummy implementations for many methods that derived
+   classes can override selectively; the default implementations represent a
+   file that cannot be read, written or seeked.
+
+   Even though :class:`IOBase` does not declare :meth:`read`, :meth:`readinto`,
+   :meth:`seek`, or :meth:`write` because their signatures will vary,
+   implementations and clients should consider those methods part of the
+   interface.  Also, implementations may raise a :exc:`IOError` when operations
+   they do not support are called.
+
+   The basic type used for binary data read from or written to a file is
+   :class:`bytes`.  :class:`bytearray`\s are accepted too, and in some cases
+   (such as :class:`readinto`) needed.  Text I/O classes work with :class:`str`
+   data.
+
+   Note that calling any method (even inquiries) on a closed file is undefined.
+   Implementations may raise :exc:`IOError` in this case.
+
+   IOBase (and its subclasses) support the iterator protocol, meaning that an
+   :class:`IOBase` object can be iterated over yielding the lines in a stream.
+
+   IOBase also supports the :keyword:`with` statement.  In this example, *fp* is
+   closed after the suite of the with statment is complete::
+
+      with open('spam.txt', 'r') as fp:
+          fp.write('Spam and eggs!')
+
+   :class:`IOBase` provides these methods:
+
+   .. method:: close()
+
+      Flush and close this stream.  This method has no effect if the file is
+      already closed.
+
+   .. attribute:: closed
+
+      True if the stream is closed.
+
+   .. method:: fileno()
+
+      Return the underlying file descriptor (an integer) of the stream, if it
+      exists.  Raises :exc:`IOError` if the IO object does not use a file
+      descriptor.
+
+   .. method:: flush()
+
+      Flush the write buffers of the stream if applicable.  This is a no-op for
+      read-only and non-blocking streams.
+
+   .. method:: isatty()
+
+      Tell if a stream is interactive (connected to a terminal/tty device).
+
+   .. method:: readable()
+
+      Tell if a stream can be read from.  If False, :meth:`read` will raise
+      :exc:`IOError`.
+
+   .. method:: readline([limit])
+
+      Read and return a line from the stream.  If *limit* is specified, at most
+      *limit* bytes will be read.
+
+      The line terminator is always ``b'\n'`` for binary files; for text files
+      the *newlines* argument to :func:`.open` can be used to select the line
+      terminator(s) recognized.
+
+   .. method:: readlines([hint])
+
+      Return a list of lines from the stream.  *hint* can be specified to
+      control the number of lines read: no more lines will be read if the total
+      size (in bytes/characters) of all lines so far exceeds *hint*.
+
+   .. method:: seekable()
+
+      Tell if a stream supports random IO access.  If ``False``, :meth:`seek`,
+      :meth:`tell` and :meth:`truncate` will raise :exc:`IOError`.
+
+   .. method:: tell()
+
+      Return an integer indicating the current stream position.
+
+   .. method:: writable()
+
+      Tell if a stream supports writing.  If ``False``, :meth:`write` and
+      :meth:`truncate` will raise :exc:`IOError`.
+
+   .. method:: writelines(lines)
+
+      Write a list of lines to the stream.  The lines will not be altered; they
+      must contain line separators.
+
+
+.. class:: RawIOBase
+
+   Base class for raw binary I/O.  It inherits :class:`IOBase`.  There is no
+   public constructor.
+
+   RawIOBase provides or overrides these methods in addition to those from
+   :class:`IOBase`:
+
+   .. method:: RawIOBase.read([n])
+
+      Read and return all bytes from the stream until EOF, or if *n* is
+      specified, up to *n* bytes.  An empty bytes object is returned on EOF;
+      ``None`` is returned if the object is set not to block and has no data to
+      read.
+
+   .. method:: RawIOBase.readall()
+
+      Read and return all bytes from the stream until EOF.
+
+
+Raw File I/O
+------------
+
+.. class:: FileIO(name[, mode])
+
+   :class:`FileIO` represents an OS file containing bytes data.  It implements
+   the :class:`RawIOBase` interface (and therefore the :class:`IOBase`
+   interface, too).
+
+   The *mode* can be ``'r'``, ``'w'`` or ``'a'`` for reading (default), writing,
+   or appending.  The file will be created if it doesn't exist when opened for
+   writing or appending; it will be truncated when opened for writing.  Add a
+   ``'+'`` to the mode to allow simultaneous reading and writing.
+
+   :class:`FileIO` provides or overrides these methods in addition to those from
+   :class:`RawIOBase` and :class:`IOBase`:
+
+   .. attribute:: mode
+
+      The mode as given in the constructor.
+
+   .. attribute:: name
+
+      The file name.
+
+   .. method:: read([n])
+
+      Read and return bytes at most *n* bytes.  Only one system call is made, so
+      less data than requested may be returned.  In non-blocking mode, ``None``
+      is returned when no data is available.
+
+   .. method:: readall()
+
+      Read and return as bytes all the data from the file.  As much as
+      immediately available is returned in non-blocking mode.  If the EOF has
+      been reached, ``b''`` is returned.
+
+   .. method:: readinto(bytearray)
+
+      This method should not be used on :class:`FileIO` objects.
+
+   .. method:: seek(offset, [whence])
+
+      Change the stream position to byte offset *pos*.  *pos* is interpreted
+      relative to the position indicated by *whence*.  Values for *whence* are:
+
+      * ``0`` -- start of stream (the default); *pos* should be zero or positive
+      * ``1`` -- current stream position; *pos* may be negative
+      * ``2`` -- end of stream; *pos* is usually negative
+
+      Return the new absolute position.
+
+   .. method:: truncate([pos])
+
+      Truncate the file to at most *pos* bytes.  *pos* defaults to the current
+      file position, as returned by :meth:`tell`.
+
+   .. method:: write(b)
+
+      Write the bytes *b* to the file, and return the number actually written.
+      Only one system call is made, so not all of the data may be written.
+
+
+Buffered Streams
+----------------
+
+.. class:: BufferedIOBase
+
+   Base class for streams that support buffering.  It inherits :class:`IOBase`.
+   There is no public constructor.
+
+   The main difference with :class:`RawIOBase` is that the :meth:`read` method
+   supports omitting the *size* argument, and does not have a default
+   implementation that defers to :meth:`readinto`.
+
+   In addition, :meth:`read`, :meth:`readinto`, and :meth:`write` may raise
+   :exc:`BlockingIOError` if the underlying raw stream is in non-blocking mode
+   and not ready; unlike their raw counterparts, they will never return
+   ``None``.
+
+   A typical implementation should not inherit from a :class:`RawIOBase`
+   implementation, but wrap one like :class:`BufferedWriter` and
+   :class:`BufferedReader`.
+
+   :class:`BufferedIOBase` provides or overrides these methods in addition to
+   those from :class:`IOBase`:
+
+   .. method:: read([n])
+
+      Read and return up to *n* bytes.  If the argument is omitted, ``None``, or
+      negative, data is read and returned until EOF is reached.  An empty bytes
+      object is returned if the stream is already at EOF.
+
+      If the argument is positive, and the underlying raw stream is not
+      interactive, multiple raw reads may be issued to satisfy the byte count
+      (unless EOF is reached first).  But for interactive raw streams, at most
+      one raw read will be issued, and a short result does not imply that EOF is
+      imminent.
+
+      A :exc:`BlockingIOError` is raised if the underlying raw stream has no
+      data at the moment.
+
+   .. method:: readinto(b)
+
+      Read up to len(b) bytes into bytearray *b* and return the number of bytes
+      read.
+
+      Like :meth:`read`, multiple reads may be issued to the underlying raw
+      stream, unless the latter is 'interactive.'
+
+      A :exc:`BlockingIOError` is raised if the underlying raw stream has no
+      data at the moment.
+
+   .. method:: seek(pos[, whence])
+
+      Change the stream position to byte offset *pos*.  *pos* is interpreted
+      relative to the position indicated by *whence*.  Values for *whence* are:
+
+      * ``0`` -- start of stream (the default); *pos* should be zero or positive
+      * ``1`` -- current stream position; *pos* may be negative
+      * ``2`` -- end of stream; *pos* is usually negative
+
+      Return the new absolute position.
+
+   .. method:: write(b)
+
+      Write the given bytes to the underlying raw stream and return the number
+      of bytes written (never less than ``len(b)``).
+
+      A :exc:`BlockingIOError` is raised if the buffer is full, and the
+      underlying raw stream cannot accept more data at the moment.
+
+
+.. class:: BytesIO([initial_bytes])
+
+   A stream implementation using an in-memory bytes buffer.  It inherits
+   :class:`BufferedIOBase`.
+
+   The argument *initial_bytes* is an optional initial bytearray.
+
+   :class:`BytesIO` provides or overrides these methods in addition to those
+   from :class:`BufferedIOBase` and :class:`IOBase`:
+
+   .. method:: getvalue()
+
+      Return the bytes value of the buffer.
+
+   .. method:: read1()
+
+      In :class:`BytesIO`, this is the same as :meth:`read`.
+
+   .. method:: truncate([pos])
+
+      Truncate the file to at most *pos* bytes.  *pos* defaults to the current
+      stream position, as returned by :meth:`tell`.
+
+
+.. class:: BufferedReader(raw, [buffer_size])
+
+   A buffer for a readable sequential RawIO object.  It inherits
+   :class:`BufferedIOBase`.
+
+   The constructor creates a :class:`BufferedReader` for the given readable
+   *raw* stream and *buffer_size*.  If *buffer_size* is omitted,
+   :data:`DEFAULT_BUFFER_SIZE` is used.
+
+   :class:`BufferedReader` provides or overrides these methods in addition to
+   those from :class:`BufferedIOBase` and :class:`IOBase`:
+
+   .. method:: peek([n])
+
+      Return bytes from a buffer without advancing the position.  The argument
+      indicates a desired minimal number of bytes; only one read on the raw
+      stream is done to satisfy it.  More than the buffer's size is never
+      returned.
+
+   .. method:: read([n])
+
+      Read and return *n* bytes, or if *n* is not given or negative, until EOF
+      or if the read call would block in non-blocking mode.
+
+   .. method:: read1(n)
+
+      Read and return up to *n* bytes with only one call on the raw stream.  If
+      at least one byte is buffered, only buffered bytes are returned.
+      Otherwise, one raw stream read call is made.
+
+
+.. class:: BufferedWriter(raw, [buffer_size, [max_buffer_size]])
+
+   A buffer for a writeable sequential RawIO object.  It inherits
+   :class:`BufferedIOBase`.
+
+   The constructor creates a :class:`BufferedWriter` for the given writeable
+   *raw* stream.  If the *buffer_size* is not given, it defaults to
+   :data:`DEAFULT_BUFFER_SIZE`.  If *max_buffer_size* is omitted, it defaults to
+   twice the buffer size.
+
+   :class:`BufferedWriter` provides or overrides these methods in addition to
+   those from :class:`BufferedIOBase` and :class:`IOBase`:
+
+   .. method:: flush()
+
+      Force bytes held in the buffer into the raw stream.  A
+      :exc:`BlockingIOError` is be raised if the raw stream blocks.
+
+   .. method:: write(b)
+
+      Write bytes *b* onto the raw stream and return the number written.  A
+      :exc:`BlockingIOError` is raised when the raw stream blocks.
+
+
+.. class:: BufferedRWPair(reader, writer, [buffer_size, [max_buffer_size]])
+
+   A buffered writer and reader object together for a raw stream that can be
+   written and read from.  It has and supports both :meth:`read`, :meth:`write`,
+   and their variants.  This is useful for such applications such as sockets and
+   two-way pipes.  It inherits :class:`BufferedIOBase`.
+
+   *reader* and *writer* are :class:`RawIOBase` objects that are readable and
+   writeable respectively.  If the *buffer_size* is omitted it defaults to
+   :data:`DEFAULT_BUFFER_SIZE`.  The *max_buffer_size* (for the buffered writer)
+   defaults to twice the buffer size.
+
+   :class:`BufferedRWPair` implements all of :class:`BufferedIOBase`\'s methods.
+
+
+.. class:: BufferedRandom(raw, [buffer_size, [max_buffer_size]])
+
+   A buffered interface to random access streams.  It inherits
+   :class:`BufferedReader` and :class:`BufferedWriter`.
+
+   The constructor creates a reader and writer for a seekable *raw* stream given
+   in the first argument.  If the *buffer_size* is omitted it defaults to
+   :data:`DEFAULT_BUFFER_SIZE`.  The *max_buffer_size* (for the buffered writer)
+   defaults to twice the buffer size.
+
+   :class:`BufferedRandom` is capable of anything :class:`BufferedReader` or
+   :class:`BufferedWriter` can do.
+
+
+Text I/O
+--------
+
+.. class:: TextIOBase
+
+   Base class for text streams.  This class provides a character and line based
+   interface to stream I/O.  There is no :meth:`readinto` method because
+   Python's character strings are immutable.  It inherits :class:`IOBase`.
+   There is no public constructor.
+
+   :class:`TextIOBase` provides or overrides these methods in addition to those
+   from :class:`IOBase`:
+
+   .. attribute:: encoding
+
+      Return the name of the encoding used to decode the stream's bytes into
+      strings, and to encode strings into bytes.
+
+   .. attribute:: newlines
+
+      Return a string, tuple of strings, or ``None`` indicating the newlines
+      translated so far.
+
+   .. method:: read(n)
+
+      Read and return at most *n* characters from the stream.  If *n* is
+      negative or ``None``, read to EOF.
+
+   .. method:: readline()
+
+      Read until newline or EOF and return.  If the stream is already at EOF, an
+      empty stream is returned.
+
+   .. method:: truncate([pos])
+
+      Truncate size to *pos*. If *pos* is not specified, it is assumed to be the
+      current position, as returned by :meth:`tell`.
+
+   .. method:: write(s)
+
+      Write string *s* to the stream and return the number of characters
+      written.
+
+
+.. class:: TextIOWrapper(buffer[, encoding[, errors[, newline[, line_buffering]]]])
+
+   A buffered text stream over a :class:`BufferedIOBase` raw stream, *buffer*.
+   It inherits :class:`TextIOBase`.
+
+   *encoding* gives the name of the encoding that the stream will be decoded or
+   encoded with.  It defaults to :func:`locale.getpreferredencoding`.
+
+   *errors* determines the strictness of encoding and decoding (see the errors
+   argument of :func:`codecs.open`) and defaults to "strict".
+
+   *newline* can be ``None``, ``''``, ``'\n'``, ``'\r'``, or ``'\r\n'``.  It
+   controls the handling of line endings.  If it is ``None``, universal newlines
+   is enabled.  With this enabled, on input, the lines endings ``'\n'``,
+   ``'\r'``, or ``'\r\n'`` are translated to ``'\n'`` before being returned to
+   the caller.  Conversely, on output, ``'\n'`` is translated to the system
+   default line seperator, :data:`os.linesep`.  If *newline* is any other of its
+   legal values, that newline becomes the newline when the file is read and it
+   is returned untranslated.  On output, ``'\n'`` is converted to the *newline*.
+
+   If *line_buffering* is ``True``, :meth:`flush` is implied when a call to
+   write contains a newline character.
+
+   :class:`TextIOWrapper` provides these methods in addition to those of
+   :class:`TextIOBase` and its parents:
+
+   .. attribute:: errors
+
+      The encoding and decoding error setting.
+
+   .. attribute:: line_buffering
+
+      Whether line buffering is enabled.
+   
+
+.. class:: StringIO([initial_value, [encoding, [errors, [newline]]]])
+
+   An in-memory stream for text.  It in inherits :class:`TextIOWrapper`.
+
+   Create a new StringIO stream with an inital value, encoding, error handling,
+   and newline setting. See :class:`TextIOWrapper`'s constructor for more
+   information.
+
+   :class:`StringIO` provides these methods in addition to those from
+   :class:`TextIOWrapper` and its parents:
+
+   .. method:: getvalue()
+
+      Return a str representation of the contents of the internal buffer.
+
+
+.. class:: IncrementalNewlineDecoder
+
+   A helper codec that decodes newlines.  It inherits
+   :class:`codecs.IncrementalDecoder`.
+