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A lot of small detailed revisions to the io module's doc.

This commit is contained in:
Mark Summerfield 2008-04-21 10:29:45 +00:00
parent a342c013fc
commit e6d5f30d1f
1 changed files with 137 additions and 117 deletions
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Doc/library/io.rst
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@ -18,19 +18,22 @@ 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:`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.
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 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.
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 @@ Module Interface
: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 @@ Module Interface
``'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 @@ Module Interface
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 @@ Module Interface
*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 @@ Module Interface
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.
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).
: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`.
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 @@ I/O Base Classes
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 @@ I/O Base Classes
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 @@ I/O Base Classes
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 @@ I/O Base Classes
.. 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 @@ I/O Base Classes
.. 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 @@ I/O Base Classes
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 @@ Raw File I/O
.. 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 @@ Raw File I/O
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 @@ Raw File I/O
.. 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 @@ Buffered Streams
.. 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 @@ Buffered Streams
.. 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 @@ Buffered Streams
.. 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 @@ Buffered Streams
.. 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 @@ Buffered Streams
.. 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 @@ Buffered Streams
.. 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 @@ Text I/O
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 @@ Text I/O
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 @@ Text I/O
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