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