Fleshed out docstrings in the io module, improving the reST one as I went.
diff --git a/Lib/io.py b/Lib/io.py
index a5c66c2..30b256f 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -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>, "
"Mike Verdone <mike.verdone@gmail.com>, "
@@ -51,62 +78,104 @@
def open(file, mode="r", buffering=None, encoding=None, errors=None,
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: string giving the name of the file to be opened;
- or integer file descriptor of the file to be wrapped (*).
- mode: optional mode string; see below.
- buffering: optional int >= 0 giving the buffer size; values
- 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:
+ file is either a string giving the name (and the path if the file
+ isn't in the current working directory) of the file to be opened or an
+ integer file descriptor of the file to be wrapped. (If a file
+ descriptor is given, it is closed when the returned I/O object is
+ closed, unless closefd is set to False.)
- * 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.
+ mode is an optional string that specifies the mode in which the file
+ is opened. It defaults to 'r' which means open for reading in text
+ mode. Other common values are 'w' for writing (truncating the file if
+ it already exists), and 'a' for appending (which on some Unix systems,
+ means that all writes append to the end of the file regardless of the
+ current seek position). In text mode, if encoding is not specified the
+ encoding used is platform dependent. (For reading and writing raw
+ bytes use binary mode and leave encoding unspecified.) The available
+ modes are:
- * 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.
+ ========= ===============================================================
+ 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)
+ ========= ===============================================================
- closefd: optional argument to keep the underlying file descriptor
- open when the file is closed. It must not be false when
- a filename is given.
+ 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.
- (*) If a file descriptor is given, it is closed when the returned
- I/O object is closed, unless closefd=False is given.
+ Python distinguishes between files opened in binary and text modes,
+ 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:
- 'r': open for reading (default)
- 'w': open for writing, truncating the file first
- 'a': open for writing, appending to the end if the file exists
- 'b': binary mode
- 't': text mode (default)
- '+': open a disk file for updating (implies reading and writing)
- 'U': universal newline mode (for backwards compatibility)
+ 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 binary mode), 1 to set line buffering, and an integer > 1
+ for full buffering.
- Constraints:
- - encoding or errors must not be given when a binary mode is given
- - buffering must not be zero when a text mode is given
+ encoding is the name of the encoding used to decode or encode the
+ file. This should only be used in text mode. The default encoding is
+ platform dependent, but any encoding supported by Python can be
+ passed. See the codecs module for the list of supported encodings.
- Returns:
- Depending on the mode and buffering arguments, either a raw
- binary stream, a buffered binary stream, or a buffered text
- stream, open for reading and/or writing.
+ errors is an optional string that specifies how encoding errors are to
+ be handled---this argument should not be used in binary mode. Pass
+ 'strict' to raise a ValueError exception if there is an encoding error
+ (the default of None has the same effect), or pass 'ignore' to ignore
+ errors. (Note that ignoring encoding errors can lead to data loss.)
+ 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)):
raise TypeError("invalid file: %r" % file)
@@ -218,18 +287,35 @@
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
- derived classes can override selectively; the default
- implementations represent a file that cannot be read, written or
- seeked.
+ derived classes can override selectively; the default implementations
+ represent a file that cannot be read, written or seeked.
- This does not define read(), readinto() and write(), nor
- readline() and friends, since their signatures vary per layer.
+ Even though IOBase does not declare read, readinto, or write because
+ 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.
+
+ 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 ###
@@ -244,11 +330,15 @@
def seek(self, pos: int, whence: int = 0) -> int:
"""seek(pos: int, whence: int = 0) -> int. Change stream position.
- Seek to byte offset pos relative to position indicated by whence:
- 0 Start of stream (the default). pos should be >= 0;
- 1 Current position - pos may be negative;
- 2 End of stream - pos usually negative.
- Returns the new absolute position.
+ 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); 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")
@@ -269,7 +359,7 @@
def flush(self) -> None:
"""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???
@@ -278,8 +368,7 @@
def close(self) -> None:
"""close() -> None. Flushes and closes the IO object.
- This must be idempotent. It should also set a flag for the
- 'closed' property (see below) to test.
+ This method has no effect if the file is already closed.
"""
if not self.__closed:
try:
@@ -385,8 +474,6 @@
def isatty(self) -> bool:
"""isatty() -> int. Returns whether this is an 'interactive' stream.
-
- Returns False if we don't know.
"""
self._checkClosed()
return False
@@ -394,7 +481,16 @@
### Readline[s] and writelines ###
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"):
def nreadahead():
readahead = self.peek(1)
@@ -430,6 +526,12 @@
return line
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:
return list(self)
n = 0
@@ -449,18 +551,17 @@
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
- classes that want to support read() only need to implement
- readinto() as a primitive operation. In general, readinto()
- can be more efficient than read().
+ # The read() method is implemented by calling readinto(); derived
+ # classes that want to support read() only need to implement
+ # readinto() as a primitive operation. In general, readinto() can be
+ # more efficient than read().
- (It would be tempting to also provide an implementation of
- readinto() in terms of read(), in case the latter is a more
- suitable primitive operation, but that would lead to nasty
- recursion in case a subclass doesn't implement either.)
- """
+ # (It would be tempting to also provide an implementation of
+ # readinto() in terms of read(), in case the latter is a more suitable
+ # primitive operation, but that would lead to nasty recursion in case
+ # a subclass doesn't implement either.)
def read(self, n: int = -1) -> bytes:
"""read(n: int) -> bytes. Read and return up to n bytes.
@@ -505,13 +606,12 @@
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
- isinstance(io.FileIO(), io.RawIOBase) return True without
- requiring that _fileio._FileIO inherits from io.RawIOBase (which
- would be hard to do since _fileio.c is written in C).
- """
+ # This multiply inherits from _FileIO and RawIOBase to make
+ # isinstance(io.FileIO(), io.RawIOBase) return True without requiring
+ # that _fileio._FileIO inherits from io.RawIOBase (which would be hard
+ # to do since _fileio.c is written in C).
def close(self):
_fileio._FileIO.close(self)
@@ -567,9 +667,8 @@
def readinto(self, b: bytearray) -> int:
"""readinto(b: bytearray) -> int. Read up to len(b) bytes into b.
- Like read(), this may issue multiple reads to the underlying
- raw stream, unless the latter is 'interactive' (XXX or a
- pipe?).
+ Like read(), this may issue multiple reads to the underlying raw
+ stream, unless the latter is 'interactive'.
Returns the number of bytes read (0 for EOF).
@@ -671,8 +770,6 @@
"""Buffered I/O implementation using an in-memory bytes buffer."""
- # XXX More docs
-
def __init__(self, initial_bytes=None):
buf = bytearray()
if initial_bytes is not None:
@@ -681,6 +778,8 @@
self._pos = 0
def getvalue(self):
+ """getvalue() -> bytes Return the bytes value (contents) of the buffer
+ """
return bytes(self._buffer)
def read(self, n=None):
@@ -694,6 +793,8 @@
return bytes(b)
def read1(self, n):
+ """In BytesIO, this is the same as read.
+ """
return self.read(n)
def write(self, b):
@@ -748,7 +849,14 @@
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):
"""Create a new buffered reader using the given readable raw IO object.
@@ -803,11 +911,9 @@
return self._read_buf
def read1(self, n):
- """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
- only return buffered bytes. Otherwise, we do one raw read.
- """
+ """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
+ # only return buffered bytes. Otherwise, we do one raw read.
if n <= 0:
return b""
self.peek(1)
@@ -826,7 +932,15 @@
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,
buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
@@ -894,15 +1008,19 @@
"""A buffered reader and writer object together.
- A buffered reader object and buffered writer object put together
- to form a sequential IO object that can read and write.
+ A buffered reader object and buffered writer object put together to
+ 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.
-
- XXX The usefulness of this (compared to having two separate IO
- objects) is questionable.
+ reader and writer are RawIOBase objects that are readable and
+ writeable respectively. 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.
"""
+ # XXX The usefulness of this (compared to having two separate IO
+ # objects) is questionable.
+
def __init__(self, reader, writer,
buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
"""Constructor.
@@ -954,7 +1072,15 @@
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,
buffer_size=DEFAULT_BUFFER_SIZE, max_buffer_size=None):
@@ -1005,9 +1131,9 @@
"""Base class for text I/O.
- This class provides a character and line based interface to stream I/O.
-
- There is no readinto() method, as character strings are immutable.
+ This class provides a character and line based interface to stream
+ I/O. There is no readinto method because Python's character strings
+ are immutable. There is no public constructor.
"""
def read(self, n: int = -1) -> str:
@@ -1055,11 +1181,11 @@
class IncrementalNewlineDecoder(codecs.IncrementalDecoder):
- """Codec used when reading a file in universal newlines mode.
- It wraps another incremental decoder, translating \\r\\n and \\r into \\n.
- It also records the types of newlines encountered.
- When used with translate=False, it ensures that the newline sequence is
- returned in one piece.
+ r"""Codec used when reading a file in universal newlines mode. It wraps
+ another incremental decoder, translating \r\n and \r into \n. It also
+ records the types of newlines encountered. When used with
+ translate=False, it ensures that the newline sequence is returned in
+ one piece.
"""
def __init__(self, decoder, translate, errors='strict'):
codecs.IncrementalDecoder.__init__(self, errors=errors)
@@ -1135,9 +1261,28 @@
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
@@ -1291,13 +1436,14 @@
def _read_chunk(self):
"""
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:
raise ValueError("no decoder")
@@ -1575,6 +1721,12 @@
return self._decoder.newlines if self._decoder else None
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