diff options
Diffstat (limited to 'Doc/library/io.rst')
| -rw-r--r-- | Doc/library/io.rst | 92 |
1 files changed, 45 insertions, 47 deletions
diff --git a/Doc/library/io.rst b/Doc/library/io.rst index 3aa2f35f05e..de5cab5aee6 100644 --- a/Doc/library/io.rst +++ b/Doc/library/io.rst @@ -528,14 +528,13 @@ I/O Base Classes It inherits from :class:`IOBase`. 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. + :meth:`readinto` and :meth:`write` will try (respectively) to read + as much input as requested or to emit all provided data. - 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``. + In addition, if the underlying raw stream is in non-blocking mode, when the + system returns would block :meth:`write` will raise :exc:`BlockingIOError` + with :attr:`BlockingIOError.characters_written` and :meth:`read` will return + data read so far or ``None`` if no data is available. Besides, the :meth:`read` method does not have a default implementation that defers to :meth:`readinto`. @@ -568,29 +567,40 @@ I/O Base Classes .. method:: read(size=-1, /) - Read and return up to *size* bytes. If the argument is omitted, ``None``, - or negative, data is read and returned until EOF is reached. An empty - :class:`bytes` object is returned if the stream is already at EOF. + Read and return up to *size* bytes. If the argument is omitted, ``None``, + or negative read as much as possible. - 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. + Fewer bytes may be returned than requested. An empty :class:`bytes` object + is returned if the stream is already at EOF. More than one read may be + made and calls may be retried if specific errors are encountered, see + :meth:`os.read` and :pep:`475` for more details. Less than size bytes + being returned does not imply that EOF is imminent. - A :exc:`BlockingIOError` is raised if the underlying raw stream is in - non blocking-mode, and has no data available at the moment. + When reading as much as possible the default implementation will use + ``raw.readall`` if available (which should implement + :meth:`RawIOBase.readall`), otherwise will read in a loop until read + returns ``None``, an empty :class:`bytes`, or a non-retryable error. For + most streams this is to EOF, but for non-blocking streams more data may + become available. + + .. note:: + + When the underlying raw stream is non-blocking, implementations may + either raise :exc:`BlockingIOError` or return ``None`` if no data is + available. :mod:`io` implementations return ``None``. .. method:: read1(size=-1, /) - Read and return up to *size* bytes, with at most one call to the - underlying raw stream's :meth:`~RawIOBase.read` (or - :meth:`~RawIOBase.readinto`) method. This can be useful if you are - implementing your own buffering on top of a :class:`BufferedIOBase` - object. + Read and return up to *size* bytes, calling :meth:`~RawIOBase.readinto` + which may retry if :py:const:`~errno.EINTR` is encountered per + :pep:`475`. If *size* is ``-1`` or not provided, the implementation will + choose an arbitrary value for *size*. - If *size* is ``-1`` (the default), an arbitrary number of bytes are - returned (more than zero unless EOF is reached). + .. note:: + + When the underlying raw stream is non-blocking, implementations may + either raise :exc:`BlockingIOError` or return ``None`` if no data is + available. :mod:`io` implementations return ``None``. .. method:: readinto(b, /) @@ -767,34 +777,21 @@ than raw I/O does. .. method:: peek(size=0, /) - 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. + Return bytes from the stream without advancing the position. The number of + bytes returned may be less or more than requested. If the underlying raw + stream is non-blocking and the operation would block, returns empty bytes. .. method:: read(size=-1, /) - Read and return *size* bytes, or if *size* is not given or negative, until - EOF or if the read call would block in non-blocking mode. - - .. note:: - - When the underlying raw stream is non-blocking, a :exc:`BlockingIOError` - may be raised if a read operation cannot be completed immediately. + In :class:`BufferedReader` this is the same as :meth:`io.BufferedIOBase.read` .. method:: read1(size=-1, /) - Read and return up to *size* 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. + In :class:`BufferedReader` this is the same as :meth:`io.BufferedIOBase.read1` .. versionchanged:: 3.7 The *size* argument is now optional. - .. note:: - - When the underlying raw stream is non-blocking, a :exc:`BlockingIOError` - may be raised if a read operation cannot be completed immediately. - .. class:: BufferedWriter(raw, buffer_size=DEFAULT_BUFFER_SIZE) A buffered binary stream providing higher-level access to a writeable, non @@ -826,8 +823,8 @@ than raw I/O does. Write the :term:`bytes-like 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. + :exc:`BlockingIOError` with :attr:`BlockingIOError.characters_written` set + is raised if the buffer needs to be written out but the raw stream blocks. .. class:: BufferedRandom(raw, buffer_size=DEFAULT_BUFFER_SIZE) @@ -894,9 +891,10 @@ Text I/O .. 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 in some implementations. + The underlying binary buffer (a :class:`BufferedIOBase` + or :class:`RawIOBase` instance) that :class:`TextIOBase` deals with. + This is not part of the :class:`TextIOBase` API and may not exist + in some implementations. .. method:: detach() |