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Sync the 2.x `io` docs with py3k, with a small note as to the distinction 

between bytes streams and text streams.
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Antoine Pitrou 2009-10-01 17:08:03 +00:00
parent dc61ec35ec
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Doc/library/io.rst
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@ -6,11 +6,23 @@
.. moduleauthor:: Guido van Rossum <guido@python.org>
.. moduleauthor:: Mike Verdone <mike.verdone@gmail.com>
.. moduleauthor:: Mark Russell <mark.russell@zen.co.uk>
.. moduleauthor:: Antoine Pitrou <solipsis@pitrou.net>
.. moduleauthor:: Amaury Forgeot d'Arc <amauryfa@gmail.com>
.. moduleauthor:: Benjamin Peterson <benjamin@python.org>
.. sectionauthor:: Benjamin Peterson <benjamin@python.org>
.. versionadded:: 2.6
The :mod:`io` module provides the Python interfaces to stream handling. The
built-in :func:`open` function is defined in this module.
The :mod:`io` module provides the Python interfaces to stream handling.
Under Python 2.x, this is proposed as an alternative to the built-in
:class:`file` object, but in Python 3.x it is the default interface to
access files and streams.
.. note::
Since this module has been designed primarily for Python 3.x, you have to
be aware that all uses of "bytes" in this document refer to the
:class:`str` type (of which :class:`bytes` is an alias), and all uses
of "text" refer to the :class:`unicode` type. Furthermore, those two
types are not interchangeable in the :mod:`io` APIs.
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
@ -31,10 +43,10 @@ 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
from and to :class:`unicode` 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.
stream for unicode text.
Argument names are not part of the specification, and only the arguments of
:func:`.open` are intended to be used as keyword arguments.
@ -49,16 +61,16 @@ Module Interface
classes. :func:`.open` uses the file's blksize (as obtained by
:func:`os.stat`) if possible.
.. function:: open(file[, mode[, buffering[, encoding[, errors[, newline[, closefd=True]]]]]])
.. function:: open(file, mode='r', buffering=None, encoding=None, errors=None, newline=None, closefd=True)
Open *file* and return a stream. If the file cannot be opened, an
:exc:`IOError` is raised.
Open *file* and return a corresponding stream. If the file cannot be opened,
an :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 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``.)
*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,
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.
@ -88,11 +100,11 @@ 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
(including ``'b'`` in the *mode* argument) return contents as ``bytes``
(including ``'b'`` in the *mode* argument) return contents as :class:`bytes`
objects without any decoding. In text mode (the default, or when ``'t'`` is
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.
:class:`unicode` strings, the bytes having been first decoded using a
platform-dependent encoding or using the specified *encoding* if given.
*buffering* is an optional integer used to set the buffering policy. By
default full buffering is on. Pass 0 to switch buffering off (only allowed
@ -101,19 +113,21 @@ 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 used. See the
:mod:`codecs` module for the list of supported encodings.
dependent (whatever :func:`locale.getpreferredencoding` returns), 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
errors are to be handled. Pass ``'strict'`` to raise a :exc:`ValueError`
exception if there is an encoding error (the default of ``None`` has the same
effect), or pass ``'ignore'`` to ignore errors. (Note that ignoring encoding
errors can lead to data loss.) ``'replace'`` causes a replacement marker
(such as ``'?'``) to be inserted where there is malformed data. When
writing, ``'xmlcharrefreplace'`` (replace with the appropriate XML character
reference) or ``'backslashreplace'`` (replace with backslashed escape
sequences) can be used. Any other error handling name that has been
registered with :func:`codecs.register_error` is also valid.
errors are to be handled--this cannot be used in binary mode. Pass
``'strict'`` to raise a :exc:`ValueError` exception if there is an encoding
error (the default of ``None`` has the same effect), or pass ``'ignore'`` to
ignore errors. (Note that ignoring encoding errors can lead to data loss.)
``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted
where there is malformed data. When writing, ``'xmlcharrefreplace'``
(replace with the appropriate XML character reference) or
``'backslashreplace'`` (replace with backslashed escape sequences) can be
used. Any other error handling name that has been registered with
:func:`codecs.register_error` is also valid.
*newline* controls how universal newlines works (it only applies to text
mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``. It
@ -133,23 +147,26 @@ Module Interface
the other legal values, any ``'\n'`` characters written are translated to
the given string.
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).
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 and 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`.
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 subclass of
:class:`TextIOBase` (specifically :class:`TextIOWrapper`). When used to open
a file in a binary mode with buffering, the returned class is a subclass of
:class:`BufferedIOBase`. The exact 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`. When buffering is disabled, the raw stream, a
subclass of :class:`RawIOBase`, :class:`FileIO`, is returned.
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 bytearrays a :class:`BytesIO` can be used like a
It is also possible to use an :class:`unicode` or :class:`bytes` string
as a file for both reading and writing. For :class:`unicode` strings
:class:`StringIO` can be used like a file opened in text mode,
and for :class:`bytes` a :class:`BytesIO` can be used like a
file opened in a binary mode.
@ -193,22 +210,25 @@ I/O Base Classes
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`) required. Text I/O classes work with
:class:`str` data.
:class:`bytes` (also known as :class:`str`). :class:`bytearray`\s are
accepted too, and in some cases (such as :class:`readinto`) required.
Text I/O classes work with :class:`unicode` data.
Note that calling any method (even inquiries) on a closed stream 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.
Lines are defined slightly differently depending on whether the stream is
a binary stream (yielding :class:`bytes`), or a text stream (yielding
:class:`unicode` strings). See :meth:`readline` below.
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', 'w') as file:
file.write('Spam and eggs!')
with io.open('spam.txt', 'w') as file:
file.write(u'Spam and eggs!')
:class:`IOBase` provides these data attributes and methods:
@ -244,7 +264,7 @@ I/O Base Classes
Return ``True`` if the stream can be read from. If False, :meth:`read`
will raise :exc:`IOError`.
.. method:: readline([limit])
.. method:: readline(limit=-1)
Read and return one line from the stream. If *limit* is specified, at
most *limit* bytes will be read.
@ -253,13 +273,13 @@ I/O Base Classes
the *newlines* argument to :func:`.open` can be used to select the line
terminator(s) recognized.
.. method:: readlines([hint])
.. method:: readlines(hint=-1)
Read and 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:: seek(offset[, whence])
.. method:: seek(offset, whence=SEEK_SET)
Change the stream position to the given byte *offset*. *offset* is
interpreted relative to the position indicated by *whence*. Values for
@ -286,7 +306,7 @@ I/O Base Classes
Return the current stream position.
.. method:: truncate([size])
.. method:: truncate(size=None)
Truncate the file to at most *size* bytes. *size* defaults to the current
file position, as returned by :meth:`tell`.
@ -308,15 +328,23 @@ I/O Base Classes
Base class for raw binary I/O. It inherits :class:`IOBase`. There is no
public constructor.
Raw binary I/O typically provides low-level access to an underlying OS
device or API, and does not try to encapsulate it in high-level primitives
(this is left to Buffered I/O and Text I/O, described later in this page).
In addition to the attributes and methods from :class:`IOBase`,
RawIOBase provides the following methods:
.. method:: read([n])
.. method:: read(n=-1)
Read and return all the bytes from the stream until EOF, or if *n* is
specified, up to *n* bytes. Only one system call is ever made. 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.
Read up to *n* bytes from the object and return them. As a convenience,
if *n* is unspecified or -1, :meth:`readall` is called. Otherwise,
only one system call is ever made. Fewer than *n* bytes may be
returned if the operating system call returns fewer than *n* bytes.
If 0 bytes are returned, and *n* was not 0, this indicates end of file.
If the object is in non-blocking mode and no bytes are available,
``None`` is returned.
.. method:: readall()
@ -331,32 +359,58 @@ I/O Base Classes
.. method:: write(b)
Write the given bytes or bytearray object, *b*, to the underlying raw
stream and return the number of bytes written (This is never less than
``len(b)``, since if the write fails, an :exc:`IOError` will be raised).
stream and return the number of bytes written. This can be less than
``len(b)``, depending on specifics of the underlying raw stream, and
especially if it is in non-blocking mode. ``None`` is returned if the
raw stream is set not to block and no single byte could be readily
written to it.
.. class:: BufferedIOBase
Base class for streams that support buffering. It inherits :class:`IOBase`.
There is no public constructor.
Base class for binary streams that support some kind of 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
The main difference with :class:`RawIOBase` is that methods :meth:`read`,
:meth:`readinto` and :meth:`write` will try (respectively) to read as much
input as requested or to consume all given output, at the expense of
making perhaps more than one system call.
In addition, those methods can raise :exc:`BlockingIOError` if the
underlying raw stream is in non-blocking mode and cannot take or give
enough data; unlike their :class:`RawIOBase` counterparts, they will
never return ``None``.
Besides, the :meth:`read` method 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 :class:`BufferedIOBase` implementation should not inherit from a
:class:`RawIOBase` implementation, but wrap one, like
:class:`BufferedWriter` and :class:`BufferedReader` do.
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
:class:`BufferedIOBase` provides or overrides these members in addition to
those from :class:`IOBase`:
.. method:: read([n])
.. attribute:: raw
The underlying raw stream (a :class:`RawIOBase` instance) that
:class:`BufferedIOBase` deals with. This is not part of the
:class:`BufferedIOBase` API and may not exist on some implementations.
.. method:: detach()
Separate the underlying raw stream from the buffer and return it.
After the raw stream has been detached, the buffer is in an unusable
state.
Some buffers, like :class:`BytesIO`, do not have the concept of a single
raw stream to return from this method. They raise
:exc:`UnsupportedOperation`.
.. versionadded:: 2.7
.. method:: read(n=-1)
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
@ -368,8 +422,15 @@ I/O Base Classes
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.
A :exc:`BlockingIOError` is raised if the underlying raw stream is in
non blocking-mode, and has no data available at the moment.
.. method:: read1(n=-1)
Read and return up to *n* bytes, with at most one call to the underlying
raw stream's :meth:`~RawIOBase.read` method. This can be useful if you
are implementing your own buffering on top of a :class:`BufferedIOBase`
object.
.. method:: readinto(b)
@ -377,35 +438,47 @@ I/O Base Classes
read.
Like :meth:`read`, multiple reads may be issued to the underlying raw
stream, unless the latter is 'interactive.'
stream, unless the latter is 'interactive'.
A :exc:`BlockingIOError` is raised if the underlying raw stream has no
data at the moment.
A :exc:`BlockingIOError` is raised if the underlying raw stream is in
non blocking-mode, and has no data available at the moment.
.. method:: write(b)
Write the given bytes or bytearray object, *b*, to the underlying raw
stream and return the number of bytes written (never less than ``len(b)``,
since if the write fails an :exc:`IOError` will be raised).
Write the given bytes or bytearray object, *b* and return the number
of bytes written (never less than ``len(b)``, since if the write fails
an :exc:`IOError` will be raised). Depending on the actual
implementation, these bytes may be readily written to the underlying
stream, or held in a buffer for performance and latency reasons.
A :exc:`BlockingIOError` is raised if the buffer is full, and the
underlying raw stream cannot accept more data at the moment.
When in non-blocking mode, a :exc:`BlockingIOError` is raised if the
data needed to be written to the raw stream but it couldn't accept
all the data without blocking.
Raw File I/O
------------
.. class:: FileIO(name[, mode])
.. class:: FileIO(name, mode='r', closefd=True)
:class:`FileIO` represents a file containing bytes data. It implements
the :class:`RawIOBase` interface (and therefore the :class:`IOBase`
interface, too).
:class:`FileIO` represents an OS-level file containing bytes data.
It implements the :class:`RawIOBase` interface (and therefore the
:class:`IOBase` interface, too).
The *name* can be one of two things:
* a string representing the path to the file which will be opened;
* an integer representing the number of an existing OS-level file descriptor
to which the resulting :class:`FileIO` object will give access.
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.
The :meth:`read` (when called with a positive argument), :meth:`readinto`
and :meth:`write` methods on this class will only make one system call.
In addition to the attributes and methods from :class:`IOBase` and
:class:`RawIOBase`, :class:`FileIO` provides the following data
attributes and methods:
@ -419,38 +492,19 @@ Raw File I/O
The file name. This is the file descriptor of the file when no name is
given in the constructor.
.. method:: read([n])
Read and return at most *n* bytes. Only one system call is made, so it is
possible that less data than was requested is returned. Use :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 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 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
----------------
In many situations, buffered I/O streams will provide higher performance
(bandwidth and latency) than raw I/O streams. Their API is also more usable.
.. 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.
The argument *initial_bytes* is an optional initial :class:`bytes`.
:class:`BytesIO` provides or overrides these methods in addition to those
from :class:`BufferedIOBase` and :class:`IOBase`:
@ -469,10 +523,13 @@ Buffered Streams
current stream position, as returned by :meth:`tell`.
.. class:: BufferedReader(raw[, buffer_size])
.. class:: BufferedReader(raw, buffer_size=DEFAULT_BUFFER_SIZE)
A buffer for a readable, sequential :class:`RawIOBase` object. It inherits
:class:`BufferedIOBase`.
A buffer providing higher-level access to a readable, sequential
:class:`RawIOBase` object. It inherits :class:`BufferedIOBase`.
When reading data from this object, a larger amount of data may be
requested from the underlying raw stream, and kept in an internal buffer.
The buffered data can then be returned directly on subsequent reads.
The constructor creates a :class:`BufferedReader` for the given readable
*raw* stream and *buffer_size*. If *buffer_size* is omitted,
@ -483,11 +540,9 @@ Buffered Streams
.. method:: peek([n])
Return 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.
Return bytes from the stream without advancing the position. At most one
single read on the raw stream is done to satisfy the call. The number of
bytes returned may be less or more than requested.
.. method:: read([n])
@ -501,15 +556,24 @@ Buffered Streams
Otherwise, one raw stream read call is made.
.. class:: BufferedWriter(raw[, buffer_size[, max_buffer_size]])
.. class:: BufferedWriter(raw, buffer_size=DEFAULT_BUFFER_SIZE)
A buffer for a writeable sequential RawIO object. It inherits
:class:`BufferedIOBase`.
A buffer providing higher-level access to a writeable, sequential
:class:`RawIOBase` object. It inherits :class:`BufferedIOBase`.
When writing to this object, data is normally held into an internal
buffer. The buffer will be written out to the underlying :class:`RawIOBase`
object under various conditions, including:
* when the buffer gets too small for all pending data;
* when :meth:`flush()` is called;
* when a :meth:`seek()` is requested (for :class:`BufferedRandom` objects);
* when the :class:`BufferedWriter` object is closed or destroyed.
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.
:data:`DEFAULT_BUFFER_SIZE`.
A third argument, *max_buffer_size*, is supported, but unused and deprecated.
:class:`BufferedWriter` provides or overrides these methods in addition to
those from :class:`BufferedIOBase` and :class:`IOBase`:
@ -521,35 +585,41 @@ Buffered Streams
.. method:: write(b)
Write the bytes or bytearray object, *b*, onto the raw stream and return
the number of bytes written. A :exc:`BlockingIOError` is raised when the
raw stream blocks.
Write the bytes or bytearray object, *b* and return the number of bytes
written. When in non-blocking mode, a :exc:`BlockingIOError` is raised
if the buffer needs to be written out but the raw stream blocks.
.. class:: BufferedRWPair(reader, writer[, buffer_size[, max_buffer_size]])
.. class:: BufferedRWPair(reader, writer, buffer_size=DEFAULT_BUFFER_SIZE)
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`.
A buffered I/O object giving a combined, higher-level access to two
sequential :class:`RawIOBase` objects: one readable, the other writeable.
It is useful for pairs of unidirectional communication channels
(pipes, for instance). 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.
:data:`DEFAULT_BUFFER_SIZE`.
:class:`BufferedRWPair` implements all of :class:`BufferedIOBase`\'s methods.
A fourth argument, *max_buffer_size*, is supported, but unused and
deprecated.
:class:`BufferedRWPair` implements all of :class:`BufferedIOBase`\'s methods
except for :meth:`~BufferedIOBase.detach`, which raises
:exc:`UnsupportedOperation`.
.. class:: BufferedRandom(raw[, buffer_size[, max_buffer_size]])
.. class:: BufferedRandom(raw, buffer_size=DEFAULT_BUFFER_SIZE)
A buffered interface to random access streams. It inherits
:class:`BufferedReader` and :class:`BufferedWriter`.
:class:`BufferedReader` and :class:`BufferedWriter`, and further supports
:meth:`seek` and :meth:`tell` functionality.
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.
:data:`DEFAULT_BUFFER_SIZE`.
A third argument, *max_buffer_size*, is supported, but unused and deprecated.
:class:`BufferedRandom` is capable of anything :class:`BufferedReader` or
:class:`BufferedWriter` can do.
@ -560,10 +630,10 @@ 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.
Base class for text streams. This class provides an unicode character
and line based interface to stream I/O. There is no :meth:`readinto`
method because Python's :class:`unicode` strings are immutable.
It inherits :class:`IOBase`. There is no public constructor.
:class:`TextIOBase` provides or overrides these data attributes and
methods in addition to those from :class:`IOBase`:
@ -580,27 +650,48 @@ Text I/O
.. attribute:: newlines
A string, a tuple of strings, or ``None``, indicating the newlines
translated so far.
translated so far. Depending on the implementation and the initial
constructor flags, this may not be available.
.. attribute:: buffer
The underlying binary buffer (a :class:`BufferedIOBase` instance) that
:class:`TextIOBase` deals with. This is not part of the
:class:`TextIOBase` API and may not exist on some implementations.
.. method:: detach()
Separate the underlying binary buffer from the :class:`TextIOBase` and
return it.
After the underlying buffer has been detached, the :class:`TextIOBase` is
in an unusable state.
Some :class:`TextIOBase` implementations, like :class:`StringIO`, may not
have the concept of an underlying buffer and calling this method will
raise :exc:`UnsupportedOperation`.
.. versionadded:: 2.7
.. method:: read(n)
Read and return at most *n* characters from the stream as a single
:class:`str`. If *n* is negative or ``None``, reads to EOF.
:class:`unicode`. If *n* is negative or ``None``, reads until EOF.
.. method:: readline()
Read until newline or EOF and return a single ``str``. If the stream is
already at EOF, an empty string is returned.
Read until newline or EOF and return a single ``unicode``. If the
stream is already at EOF, an empty string is returned.
.. method:: write(s)
Write the string *s* to the stream and return the number of characters
written.
Write the :class:`unicode` string *s* to the stream and return the
number of characters written.
.. class:: TextIOWrapper(buffer[, encoding[, errors[, newline[, line_buffering]]]])
.. class:: TextIOWrapper(buffer, encoding=None, errors=None, newline=None, line_buffering=False)
A buffered text stream over a :class:`BufferedIOBase` raw stream, *buffer*.
A buffered text stream over a :class:`BufferedIOBase` binary stream.
It inherits :class:`TextIOBase`.
*encoding* gives the name of the encoding that the stream will be decoded or
@ -637,21 +728,39 @@ Text I/O
Whether line buffering is enabled.
.. class:: StringIO([initial_value[, encoding[, errors[, newline]]]])
.. class:: StringIO(initial_value=u'', newline=None)
An in-memory stream for text. It inherits :class:`TextIOWrapper`.
An in-memory stream for unicode text. It 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.
The initial value of the buffer (an empty unicode string by default) can
be set by providing *initial_value*. The *newline* argument works like
that of :class:`TextIOWrapper`. The default is to do no newline
translation.
:class:`StringIO` provides this method in addition to those from
:class:`TextIOWrapper` and its parents:
.. method:: getvalue()
Return a ``str`` containing the entire contents of the buffer.
Return a ``unicode`` containing the entire contents of the buffer at any
time before the :class:`StringIO` object's :meth:`close` method is
called.
Example usage::
import io
output = io.StringIO()
output.write(u'First line.\n')
output.write(u'Second line.\n')
# Retrieve file contents -- this will be
# u'First line.\nSecond line.\n'
contents = output.getvalue()
# Close object and discard memory buffer --
# .getvalue() will now raise an exception.
output.close()
.. class:: IncrementalNewlineDecoder