[Python-checkins] r62430 - python/branches/py3k/Doc/library/io.rst
mark.summerfield
python-checkins at python.org
Mon Apr 21 12:29:45 CEST 2008
Author: mark.summerfield
Date: Mon Apr 21 12:29:45 2008
New Revision: 62430
Log:
A lot of small detailed revisions to the io module's doc.
Modified:
python/branches/py3k/Doc/library/io.rst
Modified: python/branches/py3k/Doc/library/io.rst
==============================================================================
--- python/branches/py3k/Doc/library/io.rst (original)
+++ python/branches/py3k/Doc/library/io.rst Mon Apr 21 12:29:45 2008
@@ -18,19 +18,22 @@
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:`RawIOBase` to provide an interface to files in the machine's
+file system.
: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.
+readable, writable, and both readable and writable.
+: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
+streams whose bytes represent text, and handles encoding and decoding
+from and to strings. :class:`TextIOWrapper`, which extends it, is a
+buffered text interface to a buffered raw stream
+(:class:`BufferedIOBase`). Finally, :class:`StringIO` is an in-memory
+stream for text.
Argument names are not part of the specification, and only the arguments of
:func:`open` are intended to be used as keyword arguments.
@@ -51,10 +54,10 @@
:exc:`IOError` is raised.
*file* is either a string giving the name (and the path if the file isn't in
- the current working directory) of the file to be opened or an integer file
- descriptor of the file to be wrapped. (If a file descriptor is given, it is
- closed when the returned I/O object is closed, unless *closefd* is set to
- ``False``.)
+ the current working directory) of the file to be opened or a file
+ descriptor of the file to be opened. (If a file descriptor is given,
+ for example, from :func:`os.fdopen`, it is closed when the returned
+ I/O object is closed, unless *closefd* is set to ``False``.)
*mode* is an optional string that specifies the mode in which the file is
opened. It defaults to ``'r'`` which means open for reading in text mode.
@@ -74,8 +77,8 @@
``'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)
+ ``'U'`` universal newline mode (for backwards compatibility; should
+ not be used in new code)
========= ===============================================================
The default mode is ``'rt'`` (open for reading text). For binary random
@@ -84,9 +87,9 @@
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) return contents as ``bytes``
+ (including ``'b'`` in the *mode* argument) 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
+ included in the *mode* argument), the contents of the file are returned as
strings, the bytes having been first decoded using a platform-dependent
encoding or using the specified *encoding* if given.
@@ -97,7 +100,7 @@
*encoding* is the name of the encoding used to decode or encode the file.
This should only be used in text mode. The default encoding is platform
- dependent, but any encoding supported by Python can be passed. See the
+ dependent, but any encoding supported by Python can be used. See the
:mod:`codecs` module for the list of supported encodings.
*errors* is an optional string that specifies how encoding and decoding
@@ -129,23 +132,24 @@
the other legal values, any ``'\n'`` characters written are translated to
the given string.
- If *closefd* is ``False``, the underlying file descriptor will be kept open
- when the file is closed. This does not work when a file name is given and
- must be ``True`` in that case.
-
- :func:`open` 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`.
+ If *closefd* is ``False`` and a file descriptor rather than a
+ filename was given, the underlying file descriptor will be kept open
+ when the file is closed. If a filename is given *closefd* has no
+ effect but must be ``True`` (the default).
+
+ The type of file object returned by the :func:`open` function depends
+ on the mode. 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:`StringIO` can be used like a file opened in
- a text mode, and for bytes a :class:`BytesIO` can be used like a file opened
- in a binary mode.
+ a text mode, and for bytearrays a :class:`BytesIO` can be used like a
+ file opened in a binary mode.
.. exception:: BlockingIOError
@@ -176,9 +180,10 @@
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.
+ This class provides empty abstract 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`,
or :meth:`write` because their signatures will vary, implementations and
@@ -188,8 +193,8 @@
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.
+ (such as :class:`readinto`) required. Text I/O classes work with
+ :class:`str` data.
Note that calling any method (even inquiries) on a closed stream is
undefined. Implementations may raise :exc:`IOError` in this case.
@@ -197,13 +202,14 @@
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::
+ IOBase is also a context manager and therefore supports the
+ :keyword:`with` statement. In this example, *file* is closed after the
+ :keyword:`with` statement's suite is finished---even if an exception occurs::
- with open('spam.txt', 'r') as fp:
- fp.write('Spam and eggs!')
+ with open('spam.txt', 'w') as file:
+ file.write('Spam and eggs!')
- :class:`IOBase` provides these methods:
+ :class:`IOBase` provides these data attributes and methods:
.. method:: close()
@@ -227,17 +233,18 @@
.. method:: isatty()
- Tell if a stream is interactive (connected to a terminal/tty device).
+ Returns ``True`` if the stream is interactive (i.e., connected to
+ a terminal/tty device).
.. method:: readable()
- Tell if a stream can be read from. If False, :meth:`read` will raise
- :exc:`IOError`.
+ Returns ``True`` if the 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.
+ Reads and returns one 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
@@ -245,45 +252,47 @@
.. method:: readlines([hint])
- Return a list of lines from the stream. *hint* can be specified to
+ Returns 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:: seek(offset[, whence])
- Change the stream position to byte offset *offset*. *offset* is
+ Change the stream position to the given byte *offset*. *offset* 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
+ * ``0`` -- start of the stream (the default); *offset* should be zero or positive
+ * ``1`` -- current stream position; *offset* may be negative
+ * ``2`` -- end of the stream; *offset* is usually negative
- Return the new absolute position.
+ Returns the new absolute position.
.. method:: seekable()
- Tell if a stream supports random IO access. If ``False``, :meth:`seek`,
- :meth:`tell` and :meth:`truncate` will raise :exc:`IOError`.
+ Returns ``True`` if the stream supports random access. If
+ ``False``, :meth:`seek`, :meth:`tell` and :meth:`truncate` will
+ raise :exc:`IOError`.
.. method:: tell()
- Return an integer indicating the current stream position.
+ Returns the current stream position.
- .. method:: truncate([pos])
+ .. method:: truncate([size])
- Truncate the file to at most *pos* bytes. *pos* defaults to the current
+ Truncates the file to at most *size* bytes. *size* defaults to the current
file position, as returned by :meth:`tell`.
.. method:: writable()
- Tell if a stream supports writing. If ``False``, :meth:`write` and
- :meth:`truncate` will raise :exc:`IOError`.
+ Returns ``True`` if the 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.
+ Writes a list of lines to the stream. Line separators are not
+ added, so it is usual for each of the lines provided to have a
+ line separator at the end.
.. class:: RawIOBase
@@ -291,30 +300,32 @@
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`:
+ In addition to the attributes and methods from :class:`IOBase`,
+ RawIOBase provides the following methods:
.. method:: read([n])
- Read and return all bytes from the stream until EOF, or if *n* is
+ Reads and returns all the 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:: readall()
- Read and return all bytes from the stream until EOF, using multiple calls
- to the stream.
+ Reads and returns all the bytes from the stream until EOF, using
+ multiple calls to the stream if necessary.
.. method:: readinto(b)
- Read up to len(b) bytes into bytearray *b* and return the number of bytes
- read.
+ Reads up to len(b) bytes into bytearray *b* and returns the number
+ of bytes read.
.. method:: write(b)
- Write the given bytes, *b*, to the underlying raw stream and return the
- number of bytes written (never less than ``len(b)``).
+ Writes the given bytes or bytearray object, *b*, to the underlying
+ raw stream and returns the number of bytes written (never less
+ than ``len(b)``, since if the write fails an :exc:`IOError` will
+ be raised).
Raw File I/O
@@ -322,7 +333,7 @@
.. class:: FileIO(name[, mode])
- :class:`FileIO` represents an OS file containing bytes data. It implements
+ :class:`FileIO` represents a file containing bytes data. It implements
the :class:`RawIOBase` interface (and therefore the :class:`IOBase`
interface, too).
@@ -331,8 +342,9 @@
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`:
+ In addition to the attributes and methods from :class:`IOBase` and
+ :class:`RawIOBase`, :class:`FileIO` provides the following data
+ attributes and methods:
.. attribute:: mode
@@ -344,24 +356,27 @@
.. 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.
+ Reads and returns at most *n* bytes. Only one system call is made, so
+ it is possible that less data than was requested is returned. Call
+ :func:`len` on the returned bytes object to see how many bytes
+ were actually 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.
+ Reads and returns the entire file's contents in a single bytes
+ object. As much as immediately available is returned in
+ non-blocking mode. If the EOF has been reached, ``b''`` is
+ returned.
.. 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.
+ Write the bytes or bytearray object, *b*, to the file, and return
+ the number actually written. Only one system call is made, so it
+ is possible that only some of the data is written.
+
+ Note that the inherited ``readinto()`` method should not be used on
+ :class:`FileIO` objects.
Buffered Streams
@@ -390,7 +405,7 @@
.. method:: read([n])
- Read and return up to *n* bytes. If the argument is omitted, ``None``, or
+ Reads and returns 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.
@@ -405,7 +420,7 @@
.. method:: readinto(b)
- Read up to len(b) bytes into bytearray *b* and return the number of bytes
+ Reads up to len(b) bytes into bytearray *b* and returns the number of bytes
read.
Like :meth:`read`, multiple reads may be issued to the underlying raw
@@ -416,8 +431,10 @@
.. method:: write(b)
- Write the given bytes, *b*, to the underlying raw stream and return the
- number of bytes written (never less than ``len(b)``).
+ Writes the given bytes or bytearray object, *b*, to the underlying
+ raw stream and returns the number of bytes written (never less than
+ ``len(b)``, since if the write fails an :exc:`IOError` will
+ be raised).
A :exc:`BlockingIOError` is raised if the buffer is full, and the
underlying raw stream cannot accept more data at the moment.
@@ -435,15 +452,16 @@
.. method:: getvalue()
- Return the bytes value of the buffer.
+ Returns a bytes object containing the entire contents of the
+ buffer.
.. method:: read1()
In :class:`BytesIO`, this is the same as :meth:`read`.
- .. method:: truncate([pos])
+ .. method:: truncate([size])
- Truncate the file to at most *pos* bytes. *pos* defaults to the current
+ Truncates the buffer to at most *size* bytes. *size* defaults to the current
stream position, as returned by :meth:`tell`.
@@ -461,19 +479,20 @@
.. 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.
+ Returns 1 (or *n* if specified) bytes from a buffer without
+ advancing the position. Only a single read on the raw stream is done to
+ satisfy the call. The number of bytes returned may be less than
+ requested since at most all the buffer's bytes from the current
+ position to the end are returned.
.. method:: read([n])
- Read and return *n* bytes, or if *n* is not given or negative, until EOF
+ Reads and returns *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
+ Reads and returns 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.
@@ -494,20 +513,21 @@
.. method:: flush()
Force bytes held in the buffer into the raw stream. A
- :exc:`BlockingIOError` is be raised if the raw stream blocks.
+ :exc:`BlockingIOError` should 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.
+ Writes the bytes or bytearray object, *b*, onto the raw stream and
+ returns the number of bytes 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`.
+ A combined buffered writer and reader object for a raw stream that can be
+ written to and read from. It has and supports both :meth:`read`, :meth:`write`,
+ and their variants. This is useful for 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
@@ -541,33 +561,33 @@
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`:
+ :class:`TextIOBase` provides or overrides these data attributes and
+ methods in addition to those from :class:`IOBase`:
.. attribute:: encoding
- Return the name of the encoding used to decode the stream's bytes into
+ 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
+ A string, a 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.
+ Reads and returns at most *n* characters from the stream as a
+ single :class:`str`. If *n* is negative or ``None``, reads to EOF.
.. method:: readline()
- Read until newline or EOF and return. If the stream is already at EOF, an
- empty stream is returned.
+ Reads until newline or EOF and returns a single :class:`str`. If
+ the stream is already at EOF, an empty string is returned.
.. method:: write(s)
- Write string *s* to the stream and return the number of characters
- written.
+ Writes the string *s* to the stream and returns the number of
+ characters written.
.. class:: TextIOWrapper(buffer[, encoding[, errors[, newline[, line_buffering]]]])
@@ -601,7 +621,7 @@
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:`TextIOWrapper` provides these data attributes in addition to those of
:class:`TextIOBase` and its parents:
.. attribute:: errors
@@ -621,12 +641,12 @@
and newline setting. See :class:`TextIOWrapper`\'s constructor for more
information.
- :class:`StringIO` provides these methods in addition to those from
+ :class:`StringIO` provides this method in addition to those from
:class:`TextIOWrapper` and its parents:
.. method:: getvalue()
- Return a str representation of the contents of the internal buffer.
+ Returns a :class:`str` containing the entire contents of the buffer.
.. class:: IncrementalNewlineDecoder
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