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Fleshed out docstrings in the io module, improving the reST one as I went.

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Benjamin Peterson 2008-04-13 00:27:46 +00:00
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143
Doc/library/io.rst
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@ -27,11 +27,14 @@ readable, writable, and both respectively. :class:`BufferedRandom` provides a
buffered interface to random access streams. :class:`BytesIO` is a simple buffered interface to random access streams. :class:`BytesIO` is a simple
stream of in-memory bytes. stream of in-memory bytes.
Another :class:`IOBase` subclass, :class:`TextIOBase` deals with the encoding Another :class:`IOBase` subclass, :class:`TextIOBase`, deals with the encoding
and decoding of streams into text. :class:`TextIOWrapper`, which extends it, is and decoding of streams into text. :class:`TextIOWrapper`, which extends it, is
a buffered text interface to a buffered raw stream (:class:`BufferedIOBase`). a buffered text interface to a buffered raw stream (:class:`BufferedIOBase`).
Finally, :class:`StringIO` is a in-memory stream for text. Finally, :class:`StringIO` is a in-memory stream for text.
Argument names are not part of the specification, and only the arguments of
:func:`open()` are intended to be used as keyword arguments.
Module Interface Module Interface
---------------- ----------------
@ -39,8 +42,8 @@ Module Interface
.. data:: DEFAULT_BUFFER_SIZE .. data:: DEFAULT_BUFFER_SIZE
An int containing the default buffer size used by the module's buffered I/O 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 classes. :func:`open()` uses the file's blksize (as obtained by
possible. :func:`os.stat`) if possible.
.. function:: open(file[, mode[, buffering[, encoding[, errors[, newline[, closefd=True]]]]]]) .. function:: open(file[, mode[, buffering[, encoding[, errors[, newline[, closefd=True]]]]]])
@ -79,18 +82,18 @@ Module Interface
access, the mode ``'w+b'`` opens and truncates the file to 0 bytes, while access, the mode ``'w+b'`` opens and truncates the file to 0 bytes, while
``'r+b'`` opens the file without truncation. ``'r+b'`` opens the file without truncation.
Python distinguishes between files opened in binary and text modes, even Python distinguishes between files opened in binary and text modes, even when
when the underlying operating system doesn't. Files opened in binary the underlying operating system doesn't. Files opened in binary mode
mode (appending ``'b'`` to the *mode* argument) return contents as (appending ``'b'`` to the *mode* argument) return contents as ``bytes``
``bytes`` objects without any decoding. In text mode (the default, or when objects without any decoding. In text mode (the default, or when ``'t'`` is
``'t'`` is appended to the *mode* argument) the contents of appended to the *mode* argument), the contents of the file are returned as
the file are returned as strings, the bytes having been first decoded strings, the bytes having been first decoded using a platform-dependent
using a platform-dependent encoding or using the specified *encoding* encoding or using the specified *encoding* if given.
if given.
*buffering* is an optional integer used to set the buffering policy. By *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 in default full buffering is on. Pass 0 to switch buffering off (only allowed
binary mode), 1 to set line buffering, and an integer > 1 for full buffering. in binary mode), 1 to set line buffering, and an integer > 1 for full
buffering.
*encoding* is the name of the encoding used to decode or encode the file. *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 This should only be used in text mode. The default encoding is platform
@ -176,18 +179,18 @@ I/O Base Classes
file that cannot be read, written or seeked. file that cannot be read, written or seeked.
Even though :class:`IOBase` does not declare :meth:`read`, :meth:`readinto`, Even though :class:`IOBase` does not declare :meth:`read`, :meth:`readinto`,
:meth:`seek`, or :meth:`write` because their signatures will vary, or :meth:`write` because their signatures will vary, implementations and
implementations and clients should consider those methods part of the clients should consider those methods part of the interface. Also,
interface. Also, implementations may raise a :exc:`IOError` when operations implementations may raise a :exc:`IOError` when operations they do not
they do not support are called. support are called.
The basic type used for binary data read from or written to a file is 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 :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` (such as :class:`readinto`) needed. Text I/O classes work with :class:`str`
data. data.
Note that calling any method (even inquiries) on a closed file is undefined. Note that calling any method (even inquiries) on a closed stream is
Implementations may raise :exc:`IOError` in this case. undefined. Implementations may raise :exc:`IOError` in this case.
IOBase (and its subclasses) support the iterator protocol, meaning that an IOBase (and its subclasses) support the iterator protocol, meaning that an
:class:`IOBase` object can be iterated over yielding the lines in a stream. :class:`IOBase` object can be iterated over yielding the lines in a stream.
@ -212,13 +215,13 @@ I/O Base Classes
.. method:: fileno() .. method:: fileno()
Return the underlying file descriptor (an integer) of the stream, if it 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 exists. An :exc:`IOError` is raised if the IO object does not use a file
descriptor. descriptor.
.. method:: flush() .. method:: flush()
Flush the write buffers of the stream if applicable. This is a no-op for Flush the write buffers of the stream if applicable. This is not
read-only and non-blocking streams. implemented for read-only and non-blocking streams.
.. method:: isatty() .. method:: isatty()
@ -234,8 +237,8 @@ I/O Base Classes
Read and return a line from the stream. If *limit* is specified, at most Read and return a line from the stream. If *limit* is specified, at most
*limit* bytes will be read. *limit* bytes will be read.
The line terminator is always ``b'\n'`` for binary files; for text files 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 the *newlines* argument to :func:`.open()` can be used to select the line
terminator(s) recognized. terminator(s) recognized.
.. method:: readlines([hint]) .. method:: readlines([hint])
@ -244,6 +247,18 @@ I/O Base Classes
control the number of lines read: no more lines will be read if the total 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*. size (in bytes/characters) of all lines so far exceeds *hint*.
.. method:: seek(offset[, whence])
Change the stream position to byte offset *offset*. *offset* is
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:: seekable() .. method:: seekable()
Tell if a stream supports random IO access. If ``False``, :meth:`seek`, Tell if a stream supports random IO access. If ``False``, :meth:`seek`,
@ -253,6 +268,11 @@ I/O Base Classes
Return an integer indicating the current stream position. Return an integer indicating the current stream 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:: writable() .. method:: writable()
Tell if a stream supports writing. If ``False``, :meth:`write` and Tell if a stream supports writing. If ``False``, :meth:`write` and
@ -281,7 +301,18 @@ I/O Base Classes
.. method:: readall() .. method:: readall()
Read and return all bytes from the stream until EOF. Read and return all bytes from the stream until EOF, using multiple calls
to the stream.
.. method:: readinto(b)
Read up to len(b) bytes into bytearray *b* and return the number of bytes
read.
.. method:: write(b)
Write the given bytes, *b*, to the underlying raw stream and return the
number of bytes written (never less than ``len(b)``).
Raw File I/O Raw File I/O
@ -325,22 +356,6 @@ Raw File I/O
This method should not be used on :class:`FileIO` objects. 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) .. method:: write(b)
Write the bytes *b* to the file, and return the number actually written. Write the bytes *b* to the file, and return the number actually written.
@ -397,21 +412,10 @@ Buffered Streams
A :exc:`BlockingIOError` is raised if the underlying raw stream has no A :exc:`BlockingIOError` is raised if the underlying raw stream has no
data at the moment. 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) .. method:: write(b)
Write the given bytes to the underlying raw stream and return the number Write the given bytes, *b*, to the underlying raw stream and return the
of bytes written (never less than ``len(b)``). number of bytes written (never less than ``len(b)``).
A :exc:`BlockingIOError` is raised if the buffer is full, and the A :exc:`BlockingIOError` is raised if the buffer is full, and the
underlying raw stream cannot accept more data at the moment. underlying raw stream cannot accept more data at the moment.
@ -433,17 +437,17 @@ Buffered Streams
.. method:: read1() .. method:: read1()
In :class:`BytesIO`, this is the same as :meth:`read`. In :class:`BytesIO`, this is the same as :meth:`read()`.
.. method:: truncate([pos]) .. method:: truncate([pos])
Truncate the file to at most *pos* bytes. *pos* defaults to the current Truncate the file to at most *pos* bytes. *pos* defaults to the current
stream position, as returned by :meth:`tell`. stream position, as returned by :meth:`tell()`.
.. class:: BufferedReader(raw, [buffer_size]) .. class:: BufferedReader(raw[, buffer_size])
A buffer for a readable sequential RawIO object. It inherits A buffer for a readable, sequential :class:`BaseRawIO` object. It inherits
:class:`BufferedIOBase`. :class:`BufferedIOBase`.
The constructor creates a :class:`BufferedReader` for the given readable The constructor creates a :class:`BufferedReader` for the given readable
@ -472,7 +476,7 @@ Buffered Streams
Otherwise, one raw stream read call is made. Otherwise, one raw stream read call is made.
.. class:: BufferedWriter(raw, [buffer_size, [max_buffer_size]]) .. class:: BufferedWriter(raw[, buffer_size[, max_buffer_size]])
A buffer for a writeable sequential RawIO object. It inherits A buffer for a writeable sequential RawIO object. It inherits
:class:`BufferedIOBase`. :class:`BufferedIOBase`.
@ -496,7 +500,7 @@ Buffered Streams
:exc:`BlockingIOError` is raised when the raw stream blocks. :exc:`BlockingIOError` is raised when the raw stream blocks.
.. class:: BufferedRWPair(reader, writer, [buffer_size, [max_buffer_size]]) .. class:: BufferedRWPair(reader, writer[, buffer_size[, max_buffer_size]])
A buffered writer and reader object together for a raw stream that can be 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`, written and read from. It has and supports both :meth:`read`, :meth:`write`,
@ -511,12 +515,12 @@ Buffered Streams
:class:`BufferedRWPair` implements all of :class:`BufferedIOBase`\'s methods. :class:`BufferedRWPair` implements all of :class:`BufferedIOBase`\'s methods.
.. class:: BufferedRandom(raw, [buffer_size, [max_buffer_size]]) .. class:: BufferedRandom(raw[, buffer_size[, max_buffer_size]])
A buffered interface to random access streams. It inherits A buffered interface to random access streams. It inherits
:class:`BufferedReader` and :class:`BufferedWriter`. :class:`BufferedReader` and :class:`BufferedWriter`.
The constructor creates a reader and writer for a seekable *raw* stream given 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 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) :data:`DEFAULT_BUFFER_SIZE`. The *max_buffer_size* (for the buffered writer)
defaults to twice the buffer size. defaults to twice the buffer size.
@ -558,11 +562,6 @@ Text I/O
Read until newline or EOF and return. If the stream is already at EOF, an Read until newline or EOF and return. If the stream is already at EOF, an
empty stream is returned. 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) .. method:: write(s)
Write string *s* to the stream and return the number of characters Write string *s* to the stream and return the number of characters
@ -578,7 +577,7 @@ Text I/O
encoded with. It defaults to :func:`locale.getpreferredencoding`. encoded with. It defaults to :func:`locale.getpreferredencoding`.
*errors* determines the strictness of encoding and decoding (see the errors *errors* determines the strictness of encoding and decoding (see the errors
argument of :func:`codecs.open`) and defaults to "strict". argument of :func:`codecs.register`) and defaults to ``'strict'``.
*newline* can be ``None``, ``''``, ``'\n'``, ``'\r'``, or ``'\r\n'``. It *newline* can be ``None``, ``''``, ``'\n'``, ``'\r'``, or ``'\r\n'``. It
controls the handling of line endings. If it is ``None``, universal newlines controls the handling of line endings. If it is ``None``, universal newlines
@ -604,12 +603,12 @@ Text I/O
Whether line buffering is enabled. Whether line buffering is enabled.
.. class:: StringIO([initial_value, [encoding, [errors, [newline]]]]) .. class:: StringIO([initial_value[, encoding[, errors[, newline]]]])
An in-memory stream for text. It in inherits :class:`TextIOWrapper`. An in-memory stream for text. It in inherits :class:`TextIOWrapper`.
Create a new StringIO stream with an inital value, encoding, error handling, Create a new StringIO stream with an inital value, encoding, error handling,
and newline setting. See :class:`TextIOWrapper`'s constructor for more and newline setting. See :class:`TextIOWrapper`\'s constructor for more
information. information.
:class:`StringIO` provides these methods in addition to those from :class:`StringIO` provides these methods in addition to those from
@ -622,6 +621,6 @@ Text I/O
.. class:: IncrementalNewlineDecoder .. class:: IncrementalNewlineDecoder
A helper codec that decodes newlines. It inherits A helper codec that decodes newlines for universal newlines mode. It
:class:`codecs.IncrementalDecoder`. inherits :class:`codecs.IncrementalDecoder`.

424
Lib/io.py
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@ -1,24 +1,51 @@
"""New I/O library conforming to PEP 3116.
This is a prototype; hopefully eventually some of this will be
reimplemented in C.
Conformance of alternative implementations: all arguments are intended
to be positional-only except the arguments of the open() function.
Argument names except those of the open() function are not part of the
specification. Instance variables and methods whose name starts with
a leading underscore are not part of the specification (except "magic"
names like __iter__). Only the top-level names listed in the __all__
variable are part of the specification.
XXX edge cases when switching between reading/writing
XXX need to support 1 meaning line-buffered
XXX whenever an argument is None, use the default value
XXX read/write ops should check readable/writable
XXX buffered readinto should work with arbitrary buffer objects
XXX use incremental encoder for text output, at least for UTF-16 and UTF-8-SIG
XXX check writable, readable and seekable in appropriate places
""" """
The io module provides the Python interfaces to stream handling. The
builtin open function is defined in this module.
At the top of the I/O hierarchy is the abstract base 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 IOError if they do not support a given operation.
Extending IOBase is RawIOBase which deals simply with the reading and
writing of raw bytes to a stream. FileIO subclasses RawIOBase to provide
an interface to OS files.
BufferedIOBase deals with buffering on a raw byte stream (RawIOBase). Its
subclasses, BufferedWriter, BufferedReader, and BufferedRWPair buffer
streams that are readable, writable, and both respectively.
BufferedRandom provides a buffered interface to random access
streams. BytesIO is a simple stream of in-memory bytes.
Another IOBase subclass, TextIOBase, deals with the encoding and decoding
of streams into text. TextIOWrapper, which extends it, is a buffered text
interface to a buffered raw stream (`BufferedIOBase`). Finally, StringIO
is a in-memory stream for text.
Argument names are not part of the specification, and only the arguments
of open() are intended to be used as keyword arguments.
data:
DEFAULT_BUFFER_SIZE
An int containing the default buffer size used by the module's buffered
I/O classes. open() uses the file's blksize (as obtained by os.stat) if
possible.
"""
# New I/O library conforming to PEP 3116.
# This is a prototype; hopefully eventually some of this will be
# reimplemented in C.
# XXX edge cases when switching between reading/writing
# XXX need to support 1 meaning line-buffered
# XXX whenever an argument is None, use the default value
# XXX read/write ops should check readable/writable
# XXX buffered readinto should work with arbitrary buffer objects
# XXX use incremental encoder for text output, at least for UTF-16 and UTF-8-SIG
# XXX check writable, readable and seekable in appropriate places
__author__ = ("Guido van Rossum <guido@python.org>, " __author__ = ("Guido van Rossum <guido@python.org>, "
"Mike Verdone <mike.verdone@gmail.com>, " "Mike Verdone <mike.verdone@gmail.com>, "
@ -51,62 +78,104 @@ class BlockingIOError(IOError):
def open(file, mode="r", buffering=None, encoding=None, errors=None, def open(file, mode="r", buffering=None, encoding=None, errors=None,
newline=None, closefd=True): newline=None, closefd=True):
r"""Replacement for the built-in open function. r"""
Open file and return a stream. If the file cannot be opened, an
IOError is raised.
Args: file is either a string giving the name (and the path if the file
file: string giving the name of the file to be opened; isn't in the current working directory) of the file to be opened or an
or integer file descriptor of the file to be wrapped (*). integer file descriptor of the file to be wrapped. (If a file
mode: optional mode string; see below. descriptor is given, it is closed when the returned I/O object is
buffering: optional int >= 0 giving the buffer size; values closed, unless closefd is set to False.)
can be: 0 = unbuffered, 1 = line buffered,
larger = fully buffered.
encoding: optional string giving the text encoding.
errors: optional string giving the encoding error handling.
newline: optional newlines specifier; must be None, '', '\n', '\r'
or '\r\n'; all other values are illegal. It controls the
handling of line endings. It works as follows:
* On input, if `newline` is `None`, universal newlines mode is an optional string that specifies the mode in which the file
mode is enabled. Lines in the input can end in `'\n'`, is opened. It defaults to 'r' which means open for reading in text
`'\r'`, or `'\r\n'`, and these are translated into mode. Other common values are 'w' for writing (truncating the file if
`'\n'` before being returned to the caller. If it is it already exists), and 'a' for appending (which on some Unix systems,
`''`, universal newline mode is enabled, but line endings means that all writes append to the end of the file regardless of the
are returned to the caller untranslated. If it has any of current seek position). In text mode, if encoding is not specified the
the other legal values, input lines are only terminated by encoding used is platform dependent. (For reading and writing raw
the given string, and the line ending is returned to the bytes use binary mode and leave encoding unspecified.) The available
caller untranslated. modes are:
* On output, if `newline` is `None`, any `'\n'` ========= ===============================================================
characters written are translated to the system default Character Meaning
line separator, `os.linesep`. If `newline` is `''`, --------- ---------------------------------------------------------------
no translation takes place. If `newline` is any of the 'r' open for reading (default)
other legal values, any `'\n'` characters written are 'w' open for writing, truncating the file first
translated to the given string. '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)
========= ===============================================================
closefd: optional argument to keep the underlying file descriptor The default mode is 'rt' (open for reading text). For binary random
open when the file is closed. It must not be false when access, the mode 'w+b' opens and truncates the file to 0 bytes, while
a filename is given. 'r+b' opens the file without truncation.
(*) If a file descriptor is given, it is closed when the returned Python distinguishes between files opened in binary and text modes,
I/O object is closed, unless closefd=False is given. even when the underlying operating system doesn't. Files opened in
binary mode (appending 'b' to the mode argument) return contents as
bytes objects without any decoding. In text mode (the default, or when
't' is appended to the mode argument), the contents of the file are
returned as strings, the bytes having been first decoded using a
platform-dependent encoding or using the specified encoding if given.
Mode strings characters: buffering is an optional integer used to set the buffering policy. By
'r': open for reading (default) default full buffering is on. Pass 0 to switch buffering off (only
'w': open for writing, truncating the file first allowed in binary mode), 1 to set line buffering, and an integer > 1
'a': open for writing, appending to the end if the file exists for full buffering.
'b': binary mode
't': text mode (default)
'+': open a disk file for updating (implies reading and writing)
'U': universal newline mode (for backwards compatibility)
Constraints: encoding is the name of the encoding used to decode or encode the
- encoding or errors must not be given when a binary mode is given file. This should only be used in text mode. The default encoding is
- buffering must not be zero when a text mode is given platform dependent, but any encoding supported by Python can be
passed. See the codecs module for the list of supported encodings.
Returns: errors is an optional string that specifies how encoding errors are to
Depending on the mode and buffering arguments, either a raw be handled---this argument should not be used in binary mode. Pass
binary stream, a buffered binary stream, or a buffered text 'strict' to raise a ValueError exception if there is an encoding error
stream, open for reading and/or writing. (the default of None has the same effect), or pass 'ignore' to ignore
errors. (Note that ignoring encoding errors can lead to data loss.)
See the documentation for codecs.register for a list of the permitted
encoding error strings.
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, 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 False, the underlying file descriptor will be kept open
when the file is closed. This does not work when a file name is given
and must be True in that case.
open() returns a file object whose type depends on the mode, and
through which the standard file operations such as reading and writing
are performed. When open() is used to open a file in a text mode ('w',
'r', 'wt', 'rt', etc.), it returns a TextIOWrapper. When used to open
a file in a binary mode, the returned class varies: in read binary
mode, it returns a BufferedReader; in write binary and append binary
modes, it returns a BufferedWriter, and in read/write mode, it returns
a BufferedRandom.
It is also possible to use a string or bytearray as a file for both
reading and writing. For strings StringIO can be used like a file
opened in a text mode, and for bytes a BytesIO can be used like a file
opened in a binary mode.
""" """
if not isinstance(file, (str, int)): if not isinstance(file, (str, int)):
raise TypeError("invalid file: %r" % file) raise TypeError("invalid file: %r" % file)
@ -218,18 +287,35 @@ class UnsupportedOperation(ValueError, IOError):
class IOBase(metaclass=abc.ABCMeta): class IOBase(metaclass=abc.ABCMeta):
"""Base class for all I/O classes. """
The abstract base class for all I/O classes, acting on streams of
bytes. There is no public constructor.
This class provides dummy implementations for many methods that This class provides dummy implementations for many methods that
derived classes can override selectively; the default derived classes can override selectively; the default implementations
implementations represent a file that cannot be read, written or represent a file that cannot be read, written or seeked.
seeked.
This does not define read(), readinto() and write(), nor Even though IOBase does not declare read, readinto, or write because
readline() and friends, since their signatures vary per layer. their signatures will vary, implementations and clients should
consider those methods part of the interface. Also, implementations
may raise a IOError when operations they do not support are called.
Note that calling any method (even inquiries) on a closed file is The basic type used for binary data read from or written to a file is
bytes. bytearrays are accepted too, and in some cases (such as
readinto) needed. Text I/O classes work with str data.
Note that calling any method (even inquiries) on a closed stream is
undefined. Implementations may raise IOError in this case. undefined. Implementations may raise IOError in this case.
IOBase (and its subclasses) support the iterator protocol, meaning
that an 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!')
""" """
### Internal ### ### Internal ###
@ -244,11 +330,15 @@ class IOBase(metaclass=abc.ABCMeta):
def seek(self, pos: int, whence: int = 0) -> int: def seek(self, pos: int, whence: int = 0) -> int:
"""seek(pos: int, whence: int = 0) -> int. Change stream position. """seek(pos: int, whence: int = 0) -> int. Change stream position.
Seek to byte offset pos relative to position indicated by whence: Change the stream position to byte offset offset. offset is
0 Start of stream (the default). pos should be >= 0; interpreted relative to the position indicated by whence. Values
1 Current position - pos may be negative; for whence are:
2 End of stream - pos usually negative.
Returns the new absolute position. * 0 -- start of stream (the default); offset should be zero or positive
* 1 -- current stream position; offset may be negative
* 2 -- end of stream; offset is usually negative
Return the new absolute position.
""" """
self._unsupported("seek") self._unsupported("seek")
@ -269,7 +359,7 @@ class IOBase(metaclass=abc.ABCMeta):
def flush(self) -> None: def flush(self) -> None:
"""flush() -> None. Flushes write buffers, if applicable. """flush() -> None. Flushes write buffers, if applicable.
This is a no-op for read-only and non-blocking streams. This is not implemented for read-only and non-blocking streams.
""" """
# XXX Should this return the number of bytes written??? # XXX Should this return the number of bytes written???
@ -278,8 +368,7 @@ class IOBase(metaclass=abc.ABCMeta):
def close(self) -> None: def close(self) -> None:
"""close() -> None. Flushes and closes the IO object. """close() -> None. Flushes and closes the IO object.
This must be idempotent. It should also set a flag for the This method has no effect if the file is already closed.
'closed' property (see below) to test.
""" """
if not self.__closed: if not self.__closed:
try: try:
@ -385,8 +474,6 @@ class IOBase(metaclass=abc.ABCMeta):
def isatty(self) -> bool: def isatty(self) -> bool:
"""isatty() -> int. Returns whether this is an 'interactive' stream. """isatty() -> int. Returns whether this is an 'interactive' stream.
Returns False if we don't know.
""" """
self._checkClosed() self._checkClosed()
return False return False
@ -394,7 +481,16 @@ class IOBase(metaclass=abc.ABCMeta):
### Readline[s] and writelines ### ### Readline[s] and writelines ###
def readline(self, limit: int = -1) -> bytes: def readline(self, limit: int = -1) -> bytes:
"""For backwards compatibility, a (slowish) readline().""" r"""readline(limit: int = -1) -> bytes 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 open can be used to select the line
terminator(s) recognized.
"""
# For backwards compatibility, a (slowish) readline().
if hasattr(self, "peek"): if hasattr(self, "peek"):
def nreadahead(): def nreadahead():
readahead = self.peek(1) readahead = self.peek(1)
@ -430,6 +526,12 @@ class IOBase(metaclass=abc.ABCMeta):
return line return line
def readlines(self, hint=None): def readlines(self, hint=None):
"""readlines(hint=None) -> list 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.
"""
if hint is None: if hint is None:
return list(self) return list(self)
n = 0 n = 0
@ -449,18 +551,17 @@ class IOBase(metaclass=abc.ABCMeta):
class RawIOBase(IOBase): class RawIOBase(IOBase):
"""Base class for raw binary I/O. """Base class for raw binary I/O."""
The read() method is implemented by calling readinto(); derived # The read() method is implemented by calling readinto(); derived
classes that want to support read() only need to implement # classes that want to support read() only need to implement
readinto() as a primitive operation. In general, readinto() # readinto() as a primitive operation. In general, readinto() can be
can be more efficient than read(). # more efficient than read().
(It would be tempting to also provide an implementation of # (It would be tempting to also provide an implementation of
readinto() in terms of read(), in case the latter is a more # readinto() in terms of read(), in case the latter is a more suitable
suitable primitive operation, but that would lead to nasty # primitive operation, but that would lead to nasty recursion in case
recursion in case a subclass doesn't implement either.) # a subclass doesn't implement either.)
"""
def read(self, n: int = -1) -> bytes: def read(self, n: int = -1) -> bytes:
"""read(n: int) -> bytes. Read and return up to n bytes. """read(n: int) -> bytes. Read and return up to n bytes.
@ -505,13 +606,12 @@ class RawIOBase(IOBase):
class FileIO(_fileio._FileIO, RawIOBase): class FileIO(_fileio._FileIO, RawIOBase):
"""Raw I/O implementation for OS files. """Raw I/O implementation for OS files."""
This multiply inherits from _FileIO and RawIOBase to make # This multiply inherits from _FileIO and RawIOBase to make
isinstance(io.FileIO(), io.RawIOBase) return True without # isinstance(io.FileIO(), io.RawIOBase) return True without requiring
requiring that _fileio._FileIO inherits from io.RawIOBase (which # that _fileio._FileIO inherits from io.RawIOBase (which would be hard
would be hard to do since _fileio.c is written in C). # to do since _fileio.c is written in C).
"""
def close(self): def close(self):
_fileio._FileIO.close(self) _fileio._FileIO.close(self)
@ -567,9 +667,8 @@ class BufferedIOBase(IOBase):
def readinto(self, b: bytearray) -> int: def readinto(self, b: bytearray) -> int:
"""readinto(b: bytearray) -> int. Read up to len(b) bytes into b. """readinto(b: bytearray) -> int. Read up to len(b) bytes into b.
Like read(), this may issue multiple reads to the underlying Like read(), this may issue multiple reads to the underlying raw
raw stream, unless the latter is 'interactive' (XXX or a stream, unless the latter is 'interactive'.
pipe?).
Returns the number of bytes read (0 for EOF). Returns the number of bytes read (0 for EOF).
@ -671,8 +770,6 @@ class BytesIO(BufferedIOBase):
"""Buffered I/O implementation using an in-memory bytes buffer.""" """Buffered I/O implementation using an in-memory bytes buffer."""
# XXX More docs
def __init__(self, initial_bytes=None): def __init__(self, initial_bytes=None):
buf = bytearray() buf = bytearray()
if initial_bytes is not None: if initial_bytes is not None:
@ -681,6 +778,8 @@ class BytesIO(BufferedIOBase):
self._pos = 0 self._pos = 0
def getvalue(self): def getvalue(self):
"""getvalue() -> bytes Return the bytes value (contents) of the buffer
"""
return bytes(self._buffer) return bytes(self._buffer)
def read(self, n=None): def read(self, n=None):
@ -694,6 +793,8 @@ class BytesIO(BufferedIOBase):
return bytes(b) return bytes(b)
def read1(self, n): def read1(self, n):
"""In BytesIO, this is the same as read.
"""
return self.read(n) return self.read(n)
def write(self, b): def write(self, b):
@ -748,7 +849,14 @@ class BytesIO(BufferedIOBase):
class BufferedReader(_BufferedIOMixin): class BufferedReader(_BufferedIOMixin):
"""Buffer for a readable sequential RawIO object.""" """BufferedReader(raw[, buffer_size])
A buffer for a readable, sequential BaseRawIO object.
The constructor creates a BufferedReader for the given readable raw
stream and buffer_size. If buffer_size is omitted, DEFAULT_BUFFER_SIZE
is used.
"""
def __init__(self, raw, buffer_size=DEFAULT_BUFFER_SIZE): def __init__(self, raw, buffer_size=DEFAULT_BUFFER_SIZE):
"""Create a new buffered reader using the given readable raw IO object. """Create a new buffered reader using the given readable raw IO object.
@ -803,11 +911,9 @@ class BufferedReader(_BufferedIOMixin):
return self._read_buf return self._read_buf
def read1(self, n): def read1(self, n):
"""Reads up to n bytes, with at most one read() system call. """Reads up to n bytes, with at most one read() system call."""
# Returns up to n bytes. If at least one byte is buffered, we
Returns up to n bytes. If at least one byte is buffered, we # only return buffered bytes. Otherwise, we do one raw read.
only return buffered bytes. Otherwise, we do one raw read.
"""
if n <= 0: if n <= 0:
return b"" return b""
self.peek(1) self.peek(1)
@ -826,7 +932,15 @@ class BufferedReader(_BufferedIOMixin):
class BufferedWriter(_BufferedIOMixin): class BufferedWriter(_BufferedIOMixin):
# XXX docstring """BufferedWriter(raw[, buffer_size[, max_buffer_size]])
A buffer for a writeable sequential RawIO object.
The constructor creates a BufferedWriter for the given writeable raw
stream. If the buffer_size is not given, it defaults to
DEAFULT_BUFFER_SIZE. If max_buffer_size is omitted, it defaults to
twice the buffer size.
"""
def __init__(self, raw, def __init__(self, raw,
buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None): buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
@ -894,15 +1008,19 @@ class BufferedRWPair(BufferedIOBase):
"""A buffered reader and writer object together. """A buffered reader and writer object together.
A buffered reader object and buffered writer object put together A buffered reader object and buffered writer object put together to
to form a sequential IO object that can read and write. form a sequential IO object that can read and write. This is typically
used with a socket or two-way pipe.
This is typically used with a socket or two-way pipe. reader and writer are RawIOBase objects that are readable and
writeable respectively. If the buffer_size is omitted it defaults to
XXX The usefulness of this (compared to having two separate IO DEFAULT_BUFFER_SIZE. The max_buffer_size (for the buffered writer)
objects) is questionable. defaults to twice the buffer size.
""" """
# XXX The usefulness of this (compared to having two separate IO
# objects) is questionable.
def __init__(self, reader, writer, def __init__(self, reader, writer,
buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None): buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
"""Constructor. """Constructor.
@ -954,7 +1072,15 @@ class BufferedRWPair(BufferedIOBase):
class BufferedRandom(BufferedWriter, BufferedReader): class BufferedRandom(BufferedWriter, BufferedReader):
# XXX docstring """BufferedRandom(raw[, buffer_size[, max_buffer_size]])
A buffered interface to random access streams.
The constructor creates a reader and writer for a seekable stream,
raw, given in the first argument. If the buffer_size is omitted it
defaults to DEFAULT_BUFFER_SIZE. The max_buffer_size (for the buffered
writer) defaults to twice the buffer size.
"""
def __init__(self, raw, def __init__(self, raw,
buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None): buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
@ -1005,9 +1131,9 @@ class TextIOBase(IOBase):
"""Base class for text I/O. """Base class for text I/O.
This class provides a character and line based interface to stream I/O. This class provides a character and line based interface to stream
I/O. There is no readinto method because Python's character strings
There is no readinto() method, as character strings are immutable. are immutable. There is no public constructor.
""" """
def read(self, n: int = -1) -> str: def read(self, n: int = -1) -> str:
@ -1055,11 +1181,11 @@ class TextIOBase(IOBase):
class IncrementalNewlineDecoder(codecs.IncrementalDecoder): class IncrementalNewlineDecoder(codecs.IncrementalDecoder):
"""Codec used when reading a file in universal newlines mode. r"""Codec used when reading a file in universal newlines mode. It wraps
It wraps another incremental decoder, translating \\r\\n and \\r into \\n. another incremental decoder, translating \r\n and \r into \n. It also
It also records the types of newlines encountered. records the types of newlines encountered. When used with
When used with translate=False, it ensures that the newline sequence is translate=False, it ensures that the newline sequence is returned in
returned in one piece. one piece.
""" """
def __init__(self, decoder, translate, errors='strict'): def __init__(self, decoder, translate, errors='strict'):
codecs.IncrementalDecoder.__init__(self, errors=errors) codecs.IncrementalDecoder.__init__(self, errors=errors)
@ -1135,9 +1261,28 @@ class IncrementalNewlineDecoder(codecs.IncrementalDecoder):
class TextIOWrapper(TextIOBase): class TextIOWrapper(TextIOBase):
"""Buffered text stream. r"""TextIOWrapper(buffer[, encoding[, errors[, newline[, line_buffering]]]])
Character and line based layer over a BufferedIOBase object. Character and line based layer over a BufferedIOBase object, buffer.
encoding gives the name of the encoding that the stream will be
decoded or encoded with. It defaults to locale.getpreferredencoding.
errors determines the strictness of encoding and decoding (see the
codecs.register) 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, 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, a call to flush is implied when a call to
write contains a newline character.
""" """
_CHUNK_SIZE = 128 _CHUNK_SIZE = 128
@ -1291,13 +1436,14 @@ class TextIOWrapper(TextIOBase):
def _read_chunk(self): def _read_chunk(self):
""" """
Read and decode the next chunk of data from the BufferedReader. Read and decode the next chunk of data from the BufferedReader.
The return value is True unless EOF was reached. The decoded string
is placed in self._decoded_chars (replacing its previous value).
The entire input chunk is sent to the decoder, though some of it
may remain buffered in the decoder, yet to be converted.
""" """
# The return value is True unless EOF was reached. The decoded
# string is placed in self._decoded_chars (replacing its previous
# value). The entire input chunk is sent to the decoder, though
# some of it may remain buffered in the decoder, yet to be
# converted.
if self._decoder is None: if self._decoder is None:
raise ValueError("no decoder") raise ValueError("no decoder")
@ -1575,6 +1721,12 @@ class TextIOWrapper(TextIOBase):
return self._decoder.newlines if self._decoder else None return self._decoder.newlines if self._decoder else None
class StringIO(TextIOWrapper): class StringIO(TextIOWrapper):
"""StringIO([initial_value[, encoding, [errors, [newline]]]])
An in-memory stream for text. The initial_value argument sets the
value of object. The other arguments are like those of TextIOWrapper's
constructor.
"""
# XXX This is really slow, but fully functional # XXX This is really slow, but fully functional