#2530: io module documentation.
This commit is contained in:
Georg Brandl
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014197caa2
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@ -14,6 +14,7 @@ but they are available on most other systems as well. Here's an overview:
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.. toctree::
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os.rst
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io.rst
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time.rst
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optparse.rst
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getopt.rst
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@ -0,0 +1,603 @@
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:mod:`io` --- Core tools for working with streams
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=================================================
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.. module:: io
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:synopsis: Core tools for working with streams.
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.. moduleauthor:: Guido van Rossum <guido@python.org>
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.. moduleauthor:: Mike Verdone <mike.verdone@gmail.com>
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.. moduleauthor:: Mark Russell <mark.russell@zen.co.uk>
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.. sectionauthor:: Benjamin Peterson
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The :mod:`io` module provides the Python interfaces to stream handling. The
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builtin :func:`open` function is defined in this module.
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At the top of the I/O hierarchy is the abstract base class :class:`IOBase`. It
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defines the basic interface to a stream. Note, however, that there is no
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seperation between reading and writing to streams; implementations are allowed
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to throw an :exc:`IOError` if they do not support a given operation.
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Extending :class:`IOBase` is :class:`RawIOBase` which deals simply with the
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reading and writing of raw bytes to a stream. :class:`FileIO` subclasses
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:class:`RawIOBase` to provide an interface to OS files.
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:class:`BufferedIOBase` deals with buffering on a raw byte stream
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(:class:`RawIOBase`). Its subclasses, :class:`BufferedWriter`,
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:class:`BufferedReader`, and :class:`BufferedRWPair` buffer streams that are
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readable, writable, and both respectively. :class:`BufferedRandom` provides a
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buffered interface to random access streams. :class:`BytesIO` is a simple
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stream of in-memory bytes.
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Another :class:`IOBase` subclass, :class:`TextIOBase` deals with the encoding
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and decoding of streams into text. :class:`TextIOWrapper`, which extends it, is
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a buffered text interface to a buffered raw stream (:class:`BufferedIOBase`).
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Finally, :class:`StringIO` is a in-memory stream for text.
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Module Interface
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----------------
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.. data:: DEFAULT_BUFFER_SIZE
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An int containing the default buffer size used by the module's buffered I/O
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classes. :func:`open` uses the file's blksize (as obtained by os.stat) if
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possible.
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.. function:: open(file[, mode[, buffering[, encoding[, errors[, newline[, closefd=True]]]]]])
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Open *file* and return a stream.
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*file* is a string giving the name of the file, or an integer file descriptor
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of the file to be wrapped.
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The optional *mode* string determines how the file is opened and consists of
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a combination of the following characters:
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========= ===============================================================
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Character Meaning
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--------- ---------------------------------------------------------------
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``'r'`` open for reading (default)
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``'w'`` open for writing, truncating the file first
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``'a'`` open for writing, appending to the end of the file if it exists
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``'b'`` binary mode
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``'t'`` text mode (default)
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``'+'`` open a disk file for updating (reading and writing)
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``'U'`` universal newline mode (for backwards compatibility; unneeded
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for new code)
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========= ===============================================================
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The default mode is ``'rt'`` (open for reading text). For binary random
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access, the mode ``'w+b'`` opens and truncates the file to 0 bytes, while
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``'r+b'`` opens the file without truncation.
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*buffering* is an optional argument controling the buffering of the returned
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stream. A value of ``0`` means no buffering, ``1`` means line buffered, and
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a greater value means full buffering with the given buffer size. Buffering
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cannot be disabled in text mode.
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*encoding* is the name of the encoding used to decode or encode the file.
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This may only be used in text mode. Any encoding available in the
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:mod:`codecs` module registry can be used.
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*errors* specifies how the encoding should treat errors. "strict", the
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default raises a :exc:`ValueError` on problems. See the *errors* argument
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of :func:`codecs.open` for more information. XXX
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*newline* controls how universal newlines works (it only applies to text
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mode). It can be ``None``, ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``. It
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works as follows:
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* On input, if *newline* is ``None``, universal newlines mode is enabled.
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Lines in the input can end in ``'\n'``, ``'\r'``, or ``'\r\n'``, and these
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are translated into ``'\n'`` before being returned to the caller. If it is
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``''``, universal newline mode is enabled, but line endings are returned to
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the caller untranslated. If it has any of the other legal values, input
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lines are only terminated by the given string, and the line ending is
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returned to the caller untranslated.
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* On output, if *newline* is ``None``, any ``'\n'`` characters written are
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translated to the system default line separator, :data:`os.linesep`. If
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*newline* is ``''``, no translation takes place. If *newline* is any of
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the other legal values, any ``'\n'`` characters written are translated to
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the given string.
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If *closefd* is :keyword:`False`, the underlying file descriptor will be kept
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open when the file is closed. This does not work when a file name is given.
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The :func:`open` function returns a file object whose type depends on the
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mode, and through which the standard file operations such as reading and
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writing are performed. When :func:`open` is used to open a file in a text
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mode (``'w'``, ``'r'``, ``'wt'``, ``'rt'``, etc.), it returns a
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:class:`TextIOWrapper`. When used to open a file in a binary mode, the
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returned class varies: in read binary mode, it returns a
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:class:`BufferedReader`; in write binary and append binary modes, it returns
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a :class:`BufferedWriter`, and in read/write mode, it returns a
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:class:`BufferedRandom`.
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It is also possible to use a string or bytearray as a file for both reading
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and writing. For strings :class:`io.StringIO` can be used like a file opened
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in a text mode, and for bytes a :class:`io.BytesIO` can be used like a file
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opened in a binary mode.
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.. exception:: BlockingIOError
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Error raised when blocking would occur on a non-blocking stream. It inherits
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:exc:`IOError`.
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In addition to those of :exc:`IOError`, :exc:`BlockingIOError` has one
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attribute:
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.. attribute:: characters_written
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An integer containing the number of characters written to the stream
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before it blocked.
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.. exception:: UnsupportedOperation
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An exception inheriting :exc:`IOError` and :exc:`ValueError` that is raised
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when an unsupported operation is called on a stream.
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I/O Base Classes
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----------------
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.. class:: IOBase
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The abstract base class for all I/O classes, acting on streams of bytes.
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There is no public constructor.
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This class provides dummy implementations for many methods that derived
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classes can override selectively; the default implementations represent a
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file that cannot be read, written or seeked.
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Even though :class:`IOBase` does not declare :meth:`read`, :meth:`readinto`,
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:meth:`seek`, or :meth:`write` because their signatures will vary,
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implementations and clients should consider those methods part of the
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interface. Also, implementations may raise a :exc:`IOError` when operations
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they do not support are called.
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The basic type used for binary data read from or written to a file is
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:class:`bytes`. :class:`bytearray`\s are accepted too, and in some cases
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(such as :class:`readinto`) needed. Text I/O classes work with :class:`str`
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data.
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Note that calling any method (even inquiries) on a closed file is undefined.
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Implementations may raise :exc:`IOError` in this case.
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IOBase (and its subclasses) support the iterator protocol, meaning that an
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:class:`IOBase` object can be iterated over yielding the lines in a stream.
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IOBase also supports the :keyword:`with` statement. In this example, *fp* is
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closed after the suite of the with statment is complete::
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with open('spam.txt', 'r') as fp:
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fp.write('Spam and eggs!')
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:class:`IOBase` provides these methods:
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.. method:: close()
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Flush and close this stream. This method has no effect if the file is
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already closed.
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.. attribute:: closed
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True if the stream is closed.
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.. method:: fileno()
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Return the underlying file descriptor (an integer) of the stream, if it
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exists. Raises :exc:`IOError` if the IO object does not use a file
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descriptor.
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.. method:: flush()
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Flush the write buffers of the stream if applicable. This is a no-op for
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read-only and non-blocking streams.
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.. method:: isatty()
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Tell if a stream is interactive (connected to a terminal/tty device).
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.. method:: readable()
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Tell if a stream can be read from. If False, :meth:`read` will raise
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:exc:`IOError`.
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.. method:: readline([limit])
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Read and return a line from the stream. If *limit* is specified, at most
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*limit* bytes will be read.
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The line terminator is always ``b'\n'`` for binary files; for text files
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the *newlines* argument to :func:`.open` can be used to select the line
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terminator(s) recognized.
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.. method:: readlines([hint])
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Return a list of lines from the stream. *hint* can be specified to
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control the number of lines read: no more lines will be read if the total
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size (in bytes/characters) of all lines so far exceeds *hint*.
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.. method:: seekable()
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Tell if a stream supports random IO access. If ``False``, :meth:`seek`,
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:meth:`tell` and :meth:`truncate` will raise :exc:`IOError`.
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.. method:: tell()
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Return an integer indicating the current stream position.
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.. method:: writable()
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Tell if a stream supports writing. If ``False``, :meth:`write` and
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:meth:`truncate` will raise :exc:`IOError`.
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.. method:: writelines(lines)
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Write a list of lines to the stream. The lines will not be altered; they
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must contain line separators.
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.. class:: RawIOBase
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Base class for raw binary I/O. It inherits :class:`IOBase`. There is no
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public constructor.
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RawIOBase provides or overrides these methods in addition to those from
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:class:`IOBase`:
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.. method:: RawIOBase.read([n])
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Read and return all bytes from the stream until EOF, or if *n* is
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specified, up to *n* bytes. An empty bytes object is returned on EOF;
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``None`` is returned if the object is set not to block and has no data to
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read.
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.. method:: RawIOBase.readall()
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Read and return all bytes from the stream until EOF.
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Raw File I/O
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------------
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.. class:: FileIO(name[, mode])
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:class:`FileIO` represents an OS file containing bytes data. It implements
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the :class:`RawIOBase` interface (and therefore the :class:`IOBase`
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interface, too).
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The *mode* can be ``'r'``, ``'w'`` or ``'a'`` for reading (default), writing,
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or appending. The file will be created if it doesn't exist when opened for
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writing or appending; it will be truncated when opened for writing. Add a
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``'+'`` to the mode to allow simultaneous reading and writing.
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:class:`FileIO` provides or overrides these methods in addition to those from
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:class:`RawIOBase` and :class:`IOBase`:
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.. attribute:: mode
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The mode as given in the constructor.
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.. attribute:: name
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The file name.
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.. method:: read([n])
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Read and return bytes at most *n* bytes. Only one system call is made, so
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less data than requested may be returned. In non-blocking mode, ``None``
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is returned when no data is available.
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.. method:: readall()
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Read and return as bytes all the data from the file. As much as
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immediately available is returned in non-blocking mode. If the EOF has
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been reached, ``b''`` is returned.
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.. method:: readinto(bytearray)
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This method should not be used on :class:`FileIO` objects.
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.. method:: seek(offset, [whence])
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Change the stream position to byte offset *pos*. *pos* is interpreted
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relative to the position indicated by *whence*. Values for *whence* are:
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* ``0`` -- start of stream (the default); *pos* should be zero or positive
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* ``1`` -- current stream position; *pos* may be negative
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* ``2`` -- end of stream; *pos* is usually negative
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Return the new absolute position.
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.. method:: truncate([pos])
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Truncate the file to at most *pos* bytes. *pos* defaults to the current
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file position, as returned by :meth:`tell`.
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.. method:: write(b)
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Write the bytes *b* to the file, and return the number actually written.
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Only one system call is made, so not all of the data may be written.
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Buffered Streams
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----------------
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.. class:: BufferedIOBase
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Base class for streams that support buffering. It inherits :class:`IOBase`.
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There is no public constructor.
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The main difference with :class:`RawIOBase` is that the :meth:`read` method
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supports omitting the *size* argument, and does not have a default
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implementation that defers to :meth:`readinto`.
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In addition, :meth:`read`, :meth:`readinto`, and :meth:`write` may raise
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:exc:`BlockingIOError` if the underlying raw stream is in non-blocking mode
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and not ready; unlike their raw counterparts, they will never return
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``None``.
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A typical implementation should not inherit from a :class:`RawIOBase`
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implementation, but wrap one like :class:`BufferedWriter` and
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:class:`BufferedReader`.
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:class:`BufferedIOBase` provides or overrides these methods in addition to
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those from :class:`IOBase`:
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.. method:: read([n])
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Read and return up to *n* bytes. If the argument is omitted, ``None``, or
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negative, data is read and returned until EOF is reached. An empty bytes
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object is returned if the stream is already at EOF.
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If the argument is positive, and the underlying raw stream is not
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interactive, multiple raw reads may be issued to satisfy the byte count
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(unless EOF is reached first). But for interactive raw streams, at most
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one raw read will be issued, and a short result does not imply that EOF is
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imminent.
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A :exc:`BlockingIOError` is raised if the underlying raw stream has no
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data at the moment.
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.. method:: readinto(b)
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Read up to len(b) bytes into bytearray *b* and return the number of bytes
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read.
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Like :meth:`read`, multiple reads may be issued to the underlying raw
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stream, unless the latter is 'interactive.'
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A :exc:`BlockingIOError` is raised if the underlying raw stream has no
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data at the moment.
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.. method:: seek(pos[, whence])
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Change the stream position to byte offset *pos*. *pos* is interpreted
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relative to the position indicated by *whence*. Values for *whence* are:
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* ``0`` -- start of stream (the default); *pos* should be zero or positive
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* ``1`` -- current stream position; *pos* may be negative
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* ``2`` -- end of stream; *pos* is usually negative
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Return the new absolute position.
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.. method:: write(b)
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Write the given bytes to the underlying raw stream and return the number
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of bytes written (never less than ``len(b)``).
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A :exc:`BlockingIOError` is raised if the buffer is full, and the
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underlying raw stream cannot accept more data at the moment.
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.. class:: BytesIO([initial_bytes])
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A stream implementation using an in-memory bytes buffer. It inherits
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:class:`BufferedIOBase`.
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The argument *initial_bytes* is an optional initial bytearray.
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:class:`BytesIO` provides or overrides these methods in addition to those
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from :class:`BufferedIOBase` and :class:`IOBase`:
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.. method:: getvalue()
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Return the bytes value of the buffer.
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.. method:: read1()
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In :class:`BytesIO`, this is the same as :meth:`read`.
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.. method:: truncate([pos])
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Truncate the file to at most *pos* bytes. *pos* defaults to the current
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stream position, as returned by :meth:`tell`.
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.. class:: BufferedReader(raw, [buffer_size])
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A buffer for a readable sequential RawIO object. It inherits
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:class:`BufferedIOBase`.
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The constructor creates a :class:`BufferedReader` for the given readable
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*raw* stream and *buffer_size*. If *buffer_size* is omitted,
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:data:`DEFAULT_BUFFER_SIZE` is used.
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:class:`BufferedReader` provides or overrides these methods in addition to
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those from :class:`BufferedIOBase` and :class:`IOBase`:
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.. method:: peek([n])
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Return bytes from a buffer without advancing the position. The argument
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indicates a desired minimal number of bytes; only one read on the raw
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stream is done to satisfy it. More than the buffer's size is never
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returned.
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.. method:: read([n])
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Read and return *n* bytes, or if *n* is not given or negative, until EOF
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or if the read call would block in non-blocking mode.
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.. method:: read1(n)
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Read and return up to *n* bytes with only one call on the raw stream. If
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at least one byte is buffered, only buffered bytes are returned.
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Otherwise, one raw stream read call is made.
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.. class:: BufferedWriter(raw, [buffer_size, [max_buffer_size]])
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A buffer for a writeable sequential RawIO object. It inherits
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:class:`BufferedIOBase`.
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The constructor creates a :class:`BufferedWriter` for the given writeable
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*raw* stream. If the *buffer_size* is not given, it defaults to
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:data:`DEAFULT_BUFFER_SIZE`. If *max_buffer_size* is omitted, it defaults to
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twice the buffer size.
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:class:`BufferedWriter` provides or overrides these methods in addition to
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those from :class:`BufferedIOBase` and :class:`IOBase`:
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.. method:: flush()
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Force bytes held in the buffer into the raw stream. A
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:exc:`BlockingIOError` is be raised if the raw stream blocks.
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.. method:: write(b)
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|
||||
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`.
|
||||
|
||||
Loading…
Reference in New Issue