io
— Outils de base pour l'utilisation des flux¶
Code source: Lib/io.py
Aperçu¶
The io
module provides Python's main facilities for dealing with various
types of I/O. There are three main types of I/O: text I/O, binary I/O
and raw I/O. These are generic categories, and various backing stores can
be used for each of them. A concrete object belonging to any of these
categories is called a file object. Other common terms are stream
and file-like object.
Independent of its category, each concrete stream object will also have various capabilities: it can be read-only, write-only, or read-write. It can also allow arbitrary random access (seeking forwards or backwards to any location), or only sequential access (for example in the case of a socket or pipe).
All streams are careful about the type of data you give to them. For example
giving a str
object to the write()
method of a binary stream
will raise a TypeError
. So will giving a bytes
object to the
write()
method of a text stream.
Modifié dans la version 3.3: Operations that used to raise IOError
now raise OSError
, since
IOError
is now an alias of OSError
.
Entrée/sortie de texte¶
Text I/O expects and produces str
objects. This means that whenever
the backing store is natively made of bytes (such as in the case of a file),
encoding and decoding of data is made transparently as well as optional
translation of platform-specific newline characters.
Le moyen le plus simple de créer un flux de texte est d'utiliser la méthode open()
en précisant éventuellement un encodage :
f = open("myfile.txt", "r", encoding="utf-8")
Les flux de texte en mémoire sont également disponible sous forme d'objets StringIO
:
f = io.StringIO("some initial text data")
L'API de flux textuel est décrite en détail dans la documentation de la classe TextIOBase
.
Binary I/O¶
Binary I/O (also called buffered I/O) expects
bytes-like objects and produces bytes
objects. No encoding, decoding, or newline translation is performed. This
category of streams can be used for all kinds of non-text data, and also when
manual control over the handling of text data is desired.
The easiest way to create a binary stream is with open()
with 'b'
in
the mode string:
f = open("myfile.jpg", "rb")
Les flux de texte en mémoire sont également disponible sous forme d'objets BytesIO
:
f = io.BytesIO(b"some initial binary data: \x00\x01")
L'API du flux binaire est décrite en détail dans la documentation de la classe BufferedIOBase
.
D'autres bibliothèques peuvent fournir des moyens supplémentaires pour créer des flux de texte ou flux binaire. Voir la méthode socket.socket.makefile()
par exemple.
Raw I/O¶
Raw I/O (also called unbuffered I/O) is generally used as a low-level building-block for binary and text streams; it is rarely useful to directly manipulate a raw stream from user code. Nevertheless, you can create a raw stream by opening a file in binary mode with buffering disabled:
f = open("myfile.jpg", "rb", buffering=0)
The raw stream API is described in detail in the docs of RawIOBase
.
Encodage de texte¶
The default encoding of TextIOWrapper
and open()
is
locale-specific (locale.getencoding()
).
However, many developers forget to specify the encoding when opening text files encoded in UTF-8 (e.g. JSON, TOML, Markdown, etc...) since most Unix platforms use UTF-8 locale by default. This causes bugs because the locale encoding is not UTF-8 for most Windows users. For example:
# May not work on Windows when non-ASCII characters in the file.
with open("README.md") as f:
long_description = f.read()
Accordingly, it is highly recommended that you specify the encoding
explicitly when opening text files. If you want to use UTF-8, pass
encoding="utf-8"
. To use the current locale encoding,
encoding="locale"
is supported since Python 3.10.
Voir aussi
- Python UTF-8 Mode
Le mode UTF-8 de Python peut être utilisé pour changer l'encodage par défaut en UTF-8 à partir d'un encodage local spécifique.
- PEP 686
Python 3.15 will make Python UTF-8 Mode default.
Opt-in EncodingWarning¶
Nouveau dans la version 3.10: See PEP 597 for more details.
To find where the default locale encoding is used, you can enable
the -X warn_default_encoding
command line option or set the
PYTHONWARNDEFAULTENCODING
environment variable, which will
emit an EncodingWarning
when the default encoding is used.
If you are providing an API that uses open()
or
TextIOWrapper
and passes encoding=None
as a parameter, you
can use text_encoding()
so that callers of the API will emit an
EncodingWarning
if they don't pass an encoding
. However,
please consider using UTF-8 by default (i.e. encoding="utf-8"
) for
new APIs.
Interface de haut niveau du module¶
- io.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 byos.stat()
) if possible.
- io.open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)¶
This is an alias for the builtin
open()
function.This function raises an auditing event
open
with arguments path, mode and flags. The mode and flags arguments may have been modified or inferred from the original call.
- io.open_code(path)¶
Opens the provided file with mode
'rb'
. This function should be used when the intent is to treat the contents as executable code.path should be a
str
and an absolute path.The behavior of this function may be overridden by an earlier call to the
PyFile_SetOpenCodeHook()
. However, assuming that path is astr
and an absolute path,open_code(path)
should always behave the same asopen(path, 'rb')
. Overriding the behavior is intended for additional validation or preprocessing of the file.Nouveau dans la version 3.8.
- io.text_encoding(encoding, stacklevel=2, /)¶
This is a helper function for callables that use
open()
orTextIOWrapper
and have anencoding=None
parameter.This function returns encoding if it is not
None
. Otherwise, it returns"locale"
or"utf-8"
depending on UTF-8 Mode.This function emits an
EncodingWarning
ifsys.flags.warn_default_encoding
is true and encoding isNone
. stacklevel specifies where the warning is emitted. For example:def read_text(path, encoding=None): encoding = io.text_encoding(encoding) # stacklevel=2 with open(path, encoding) as f: return f.read()
In this example, an
EncodingWarning
is emitted for the caller ofread_text()
.See Encodage de texte for more information.
Nouveau dans la version 3.10.
Modifié dans la version 3.11:
text_encoding()
returns "utf-8" when UTF-8 mode is enabled and encoding isNone
.
- exception io.BlockingIOError¶
This is a compatibility alias for the builtin
BlockingIOError
exception.
- exception io.UnsupportedOperation¶
An exception inheriting
OSError
andValueError
that is raised when an unsupported operation is called on a stream.
Voir aussi
sys
contains the standard IO streams:
sys.stdin
,sys.stdout
, andsys.stderr
.
Class hierarchy¶
The implementation of I/O streams is organized as a hierarchy of classes. First abstract base classes (ABCs), which are used to specify the various categories of streams, then concrete classes providing the standard stream implementations.
Note
The abstract base classes also provide default implementations of some
methods in order to help implementation of concrete stream classes. For
example, BufferedIOBase
provides unoptimized implementations of
readinto()
and readline()
.
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
separation between reading and writing to streams; implementations are allowed
to raise UnsupportedOperation
if they do not support a given operation.
The RawIOBase
ABC extends IOBase
. It deals with the reading
and writing of bytes to a stream. FileIO
subclasses RawIOBase
to provide an interface to files in the machine's file system.
The BufferedIOBase
ABC extends IOBase
. It deals with
buffering on a raw binary stream (RawIOBase
). Its subclasses,
BufferedWriter
, BufferedReader
, and BufferedRWPair
buffer raw binary streams that are writable, readable, and both readable and writable,
respectively. BufferedRandom
provides a buffered interface to seekable streams.
Another BufferedIOBase
subclass, BytesIO
, is a stream of
in-memory bytes.
The TextIOBase
ABC extends IOBase
. It deals with
streams whose bytes represent text, and handles encoding and decoding to and
from strings. TextIOWrapper
, which extends TextIOBase
, is a buffered text
interface to a buffered raw stream (BufferedIOBase
). Finally,
StringIO
is an 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.
The following table summarizes the ABCs provided by the io
module:
ABC |
Inherits |
Stub Methods |
Méthodes et propriétés de Mixin |
---|---|---|---|
|
|
||
|
Inherited |
||
|
Inherited |
||
|
Inherited |
I/O Base Classes¶
- class io.IOBase¶
The abstract base class for all I/O classes.
This class provides empty abstract 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
IOBase
does not declareread()
orwrite()
because their signatures will vary, implementations and clients should consider those methods part of the interface. Also, implementations may raise aValueError
(orUnsupportedOperation
) when operations they do not support are called.The basic type used for binary data read from or written to a file is
bytes
. Other bytes-like objects are accepted as method arguments too. Text I/O classes work withstr
data.Note that calling any method (even inquiries) on a closed stream is undefined. Implementations may raise
ValueError
in this case.IOBase
(and its subclasses) supports the iterator protocol, meaning that anIOBase
object can be iterated over yielding the lines in a stream. Lines are defined slightly differently depending on whether the stream is a binary stream (yielding bytes), or a text stream (yielding character strings). Seereadline()
below.IOBase
is also a context manager and therefore supports thewith
statement. In this example, file is closed after thewith
statement's suite is finished---even if an exception occurs:with open('spam.txt', 'w') as file: file.write('Spam and eggs!')
IOBase
provides these data attributes and methods:- close()¶
Flush and close this stream. This method has no effect if the file is already closed. Once the file is closed, any operation on the file (e.g. reading or writing) will raise a
ValueError
.As a convenience, it is allowed to call this method more than once; only the first call, however, will have an effect.
- closed¶
True
if the stream is closed.
- fileno()¶
Return the underlying file descriptor (an integer) of the stream if it exists. An
OSError
is raised if the IO object does not use a file descriptor.
- flush()¶
Flush the write buffers of the stream if applicable. This does nothing for read-only and non-blocking streams.
- isatty()¶
Return
True
if the stream is interactive (i.e., connected to a terminal/tty device).
- readline(size=-1, /)¶
Read and return one line from the stream. If size is specified, at most size bytes will be read.
The line terminator is always
b'\n'
for binary files; for text files, the newline argument toopen()
can be used to select the line terminator(s) recognized.
- readlines(hint=-1, /)¶
Read and 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.
hint values of
0
or less, as well asNone
, are treated as no hint.Note that it's already possible to iterate on file objects using
for line in file: ...
without callingfile.readlines()
.
- seek(offset, whence=os.SEEK_SET, /)¶
Change the stream position to the given byte offset, interpreted relative to the position indicated by whence, and return the new absolute position. Values for whence are:
os.SEEK_SET
or0
-- start of the stream (the default); offset should be zero or positiveos.SEEK_CUR
or1
-- current stream position; offset may be negativeos.SEEK_END
or2
-- end of the stream; offset is usually negative
Nouveau dans la version 3.1: The
SEEK_*
constants.Nouveau dans la version 3.3: Some operating systems could support additional values, like
os.SEEK_HOLE
oros.SEEK_DATA
. The valid values for a file could depend on it being open in text or binary mode.
- seekable()¶
Return
True
if the stream supports random access. IfFalse
,seek()
,tell()
andtruncate()
will raiseOSError
.
- tell()¶
Return the current stream position.
- truncate(size=None, /)¶
Resize the stream to the given size in bytes (or the current position if size is not specified). The current stream position isn't changed. This resizing can extend or reduce the current file size. In case of extension, the contents of the new file area depend on the platform (on most systems, additional bytes are zero-filled). The new file size is returned.
Modifié dans la version 3.5: Windows will now zero-fill files when extending.
- writable()¶
Return
True
if the stream supports writing. IfFalse
,write()
andtruncate()
will raiseOSError
.
- writelines(lines, /)¶
Write a list of lines to the stream. Line separators are not added, so it is usual for each of the lines provided to have a line separator at the end.
- class io.RawIOBase¶
Base class for raw binary streams. It inherits from
IOBase
.Raw binary streams typically provide low-level access to an underlying OS device or API, and do not try to encapsulate it in high-level primitives (this functionality is done at a higher-level in buffered binary streams and text streams, described later in this page).
RawIOBase
provides these methods in addition to those fromIOBase
:- read(size=-1, /)¶
Read up to size bytes from the object and return them. As a convenience, if size is unspecified or -1, all bytes until EOF are returned. Otherwise, only one system call is ever made. Fewer than size bytes may be returned if the operating system call returns fewer than size bytes.
If 0 bytes are returned, and size was not 0, this indicates end of file. If the object is in non-blocking mode and no bytes are available,
None
is returned.The default implementation defers to
readall()
andreadinto()
.
- readall()¶
Read and return all the bytes from the stream until EOF, using multiple calls to the stream if necessary.
- readinto(b, /)¶
Read bytes into a pre-allocated, writable bytes-like object b, and return the number of bytes read. For example, b might be a
bytearray
. If the object is in non-blocking mode and no bytes are available,None
is returned.
- write(b, /)¶
Write the given bytes-like object, b, to the underlying raw stream, and return the number of bytes written. This can be less than the length of b in bytes, depending on specifics of the underlying raw stream, and especially if it is in non-blocking mode.
None
is returned if the raw stream is set not to block and no single byte could be readily written to it. The caller may release or mutate b after this method returns, so the implementation should only access b during the method call.
- class io.BufferedIOBase¶
Base class for binary streams that support some kind of buffering. It inherits from
IOBase
.The main difference with
RawIOBase
is that methodsread()
,readinto()
andwrite()
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.In addition, those methods can raise
BlockingIOError
if the underlying raw stream is in non-blocking mode and cannot take or give enough data; unlike theirRawIOBase
counterparts, they will never returnNone
.Besides, the
read()
method does not have a default implementation that defers toreadinto()
.A typical
BufferedIOBase
implementation should not inherit from aRawIOBase
implementation, but wrap one, likeBufferedWriter
andBufferedReader
do.BufferedIOBase
provides or overrides these data attributes and methods in addition to those fromIOBase
:- raw¶
The underlying raw stream (a
RawIOBase
instance) thatBufferedIOBase
deals with. This is not part of theBufferedIOBase
API and may not exist on some implementations.
- detach()¶
Sépare le flux brut sous-jacent du tampon et le renvoie.
After the raw stream has been detached, the buffer is in an unusable state.
Some buffers, like
BytesIO
, do not have the concept of a single raw stream to return from this method. They raiseUnsupportedOperation
.Nouveau dans la version 3.1.
- 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 emptybytes
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
BlockingIOError
is raised if the underlying raw stream is in non blocking-mode, and has no data available at the moment.
- read1(size=-1, /)¶
Read and return up to size bytes, with at most one call to the underlying raw stream's
read()
(orreadinto()
) method. This can be useful if you are implementing your own buffering on top of aBufferedIOBase
object.If size is
-1
(the default), an arbitrary number of bytes are returned (more than zero unless EOF is reached).
- readinto(b, /)¶
Read bytes into a pre-allocated, writable bytes-like object b and return the number of bytes read. For example, b might be a
bytearray
.Like
read()
, multiple reads may be issued to the underlying raw stream, unless the latter is interactive.A
BlockingIOError
is raised if the underlying raw stream is in non blocking-mode, and has no data available at the moment.
- readinto1(b, /)¶
Read bytes into a pre-allocated, writable bytes-like object b, using at most one call to the underlying raw stream's
read()
(orreadinto()
) method. Return the number of bytes read.A
BlockingIOError
is raised if the underlying raw stream is in non blocking-mode, and has no data available at the moment.Nouveau dans la version 3.5.
- write(b, /)¶
Write the given bytes-like object, b, and return the number of bytes written (always equal to the length of b in bytes, since if the write fails an
OSError
will be raised). Depending on the actual implementation, these bytes may be readily written to the underlying stream, or held in a buffer for performance and latency reasons.When in non-blocking mode, a
BlockingIOError
is raised if the data needed to be written to the raw stream but it couldn't accept all the data without blocking.The caller may release or mutate b after this method returns, so the implementation should only access b during the method call.
Raw File I/O¶
- class io.FileIO(name, mode='r', closefd=True, opener=None)¶
A raw binary stream representing an OS-level file containing bytes data. It inherits from
RawIOBase
.The name can be one of two things:
a character string or
bytes
object representing the path to the file which will be opened. In this case closefd must beTrue
(the default) otherwise an error will be raised.an integer representing the number of an existing OS-level file descriptor to which the resulting
FileIO
object will give access. When the FileIO object is closed this fd will be closed as well, unless closefd is set toFalse
.
The mode can be
'r'
,'w'
,'x'
or'a'
for reading (default), writing, exclusive creation 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.FileExistsError
will be raised if it already exists when opened for creating. Opening a file for creating implies writing, so this mode behaves in a similar way to'w'
. Add a'+'
to the mode to allow simultaneous reading and writing.The
read()
(when called with a positive argument),readinto()
andwrite()
methods on this class will only make one system call.Un opener personnalisé peut être utilisé en fournissant un appelable à opener. Le descripteur de fichier de cet objet fichier sera alors obtenu en appelant opener avec (file, flags). opener doit donner un descripteur de fichier ouvert (fournir
os.open
en temps qu'opener aura le même effet que donnerNone
).Il n'est pas possible d'hériter du fichier nouvellement créé.
See the
open()
built-in function for examples on using the opener parameter.Modifié dans la version 3.3: The opener parameter was added. The
'x'
mode was added.Modifié dans la version 3.4: Il n'est plus possible d'hériter de file.
FileIO
provides these data attributes in addition to those fromRawIOBase
andIOBase
:- mode¶
The mode as given in the constructor.
- name¶
Le nom du fichier. C'est le descripteur du fichier lorsqu'aucun nom n'est donné dans le constructeur.
Buffered Streams¶
Buffered I/O streams provide a higher-level interface to an I/O device than raw I/O does.
- class io.BytesIO(initial_bytes=b'')¶
A binary stream using an in-memory bytes buffer. It inherits from
BufferedIOBase
. The buffer is discarded when theclose()
method is called.The optional argument initial_bytes is a bytes-like object that contains initial data.
BytesIO
provides or overrides these methods in addition to those fromBufferedIOBase
andIOBase
:- getbuffer()¶
Return a readable and writable view over the contents of the buffer without copying them. Also, mutating the view will transparently update the contents of the buffer:
>>> b = io.BytesIO(b"abcdef") >>> view = b.getbuffer() >>> view[2:4] = b"56" >>> b.getvalue() b'ab56ef'
Note
As long as the view exists, the
BytesIO
object cannot be resized or closed.Nouveau dans la version 3.2.
- read1(size=-1, /)¶
In
BytesIO
, this is the same asread()
.Modifié dans la version 3.7: The size argument is now optional.
- readinto1(b, /)¶
In
BytesIO
, this is the same asreadinto()
.Nouveau dans la version 3.5.
- class io.BufferedReader(raw, buffer_size=DEFAULT_BUFFER_SIZE)¶
A buffered binary stream providing higher-level access to a readable, non seekable
RawIOBase
raw binary stream. It inherits fromBufferedIOBase
.When reading data from this object, a larger amount of data may be requested from the underlying raw stream, and kept in an internal buffer. The buffered data can then be returned directly on subsequent reads.
The constructor creates a
BufferedReader
for the given readable raw stream and buffer_size. If buffer_size is omitted,DEFAULT_BUFFER_SIZE
is used.BufferedReader
provides or overrides these methods in addition to those fromBufferedIOBase
andIOBase
:- 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.
- 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.
- 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.
Modifié dans la version 3.7: The size argument is now optional.
- class io.BufferedWriter(raw, buffer_size=DEFAULT_BUFFER_SIZE)¶
A buffered binary stream providing higher-level access to a writeable, non seekable
RawIOBase
raw binary stream. It inherits fromBufferedIOBase
.When writing to this object, data is normally placed into an internal buffer. The buffer will be written out to the underlying
RawIOBase
object under various conditions, including:when the buffer gets too small for all pending data;
when
flush()
is called;when a
seek()
is requested (forBufferedRandom
objects);when the
BufferedWriter
object is closed or destroyed.
The constructor creates a
BufferedWriter
for the given writeable raw stream. If the buffer_size is not given, it defaults toDEFAULT_BUFFER_SIZE
.BufferedWriter
provides or overrides these methods in addition to those fromBufferedIOBase
andIOBase
:- flush()¶
Force bytes held in the buffer into the raw stream. A
BlockingIOError
should be raised if the raw stream blocks.
- write(b, /)¶
Write the bytes-like object, b, and return the number of bytes written. When in non-blocking mode, a
BlockingIOError
is raised if the buffer needs to be written out but the raw stream blocks.
- class io.BufferedRandom(raw, buffer_size=DEFAULT_BUFFER_SIZE)¶
A buffered binary stream providing higher-level access to a seekable
RawIOBase
raw binary stream. It inherits fromBufferedReader
andBufferedWriter
.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
DEFAULT_BUFFER_SIZE
.BufferedRandom
is capable of anythingBufferedReader
orBufferedWriter
can do. In addition,seek()
andtell()
are guaranteed to be implemented.
- class io.BufferedRWPair(reader, writer, buffer_size=DEFAULT_BUFFER_SIZE, /)¶
A buffered binary stream providing higher-level access to two non seekable
RawIOBase
raw binary streams---one readable, the other writeable. It inherits fromBufferedIOBase
.reader and writer are
RawIOBase
objects that are readable and writeable respectively. If the buffer_size is omitted it defaults toDEFAULT_BUFFER_SIZE
.BufferedRWPair
implements all ofBufferedIOBase
's methods except fordetach()
, which raisesUnsupportedOperation
.Avertissement
BufferedRWPair
does not attempt to synchronize accesses to its underlying raw streams. You should not pass it the same object as reader and writer; useBufferedRandom
instead.
Entrée/sortie de texte¶
- class io.TextIOBase¶
Base class for text streams. This class provides a character and line based interface to stream I/O. It inherits from
IOBase
.TextIOBase
provides or overrides these data attributes and methods in addition to those fromIOBase
:- encoding¶
The name of the encoding used to decode the stream's bytes into strings, and to encode strings into bytes.
- errors¶
The error setting of the decoder or encoder.
- newlines¶
A string, a tuple of strings, or
None
, indicating the newlines translated so far. Depending on the implementation and the initial constructor flags, this may not be available.
- buffer¶
The underlying binary buffer (a
BufferedIOBase
instance) thatTextIOBase
deals with. This is not part of theTextIOBase
API and may not exist in some implementations.
- detach()¶
Separate the underlying binary buffer from the
TextIOBase
and return it.After the underlying buffer has been detached, the
TextIOBase
is in an unusable state.Some
TextIOBase
implementations, likeStringIO
, may not have the concept of an underlying buffer and calling this method will raiseUnsupportedOperation
.Nouveau dans la version 3.1.
- read(size=-1, /)¶
Read and return at most size characters from the stream as a single
str
. If size is negative orNone
, reads until EOF.
- readline(size=-1, /)¶
Read until newline or EOF and return a single
str
. If the stream is already at EOF, an empty string is returned.If size is specified, at most size characters will be read.
- seek(offset, whence=SEEK_SET, /)¶
Change the stream position to the given offset. Behaviour depends on the whence parameter. The default value for whence is
SEEK_SET
.SEEK_SET
or0
: seek from the start of the stream (the default); offset must either be a number returned byTextIOBase.tell()
, or zero. Any other offset value produces undefined behaviour.SEEK_CUR
or1
: "seek" to the current position; offset must be zero, which is a no-operation (all other values are unsupported).SEEK_END
or2
: seek to the end of the stream; offset must be zero (all other values are unsupported).
Return the new absolute position as an opaque number.
Nouveau dans la version 3.1: The
SEEK_*
constants.
- tell()¶
Return the current stream position as an opaque number. The number does not usually represent a number of bytes in the underlying binary storage.
- write(s, /)¶
Write the string s to the stream and return the number of characters written.
- class io.TextIOWrapper(buffer, encoding=None, errors=None, newline=None, line_buffering=False, write_through=False)¶
A buffered text stream providing higher-level access to a
BufferedIOBase
buffered binary stream. It inherits fromTextIOBase
.encoding gives the name of the encoding that the stream will be decoded or encoded with. It defaults to
locale.getencoding()
.encoding="locale"
can be used to specify the current locale's encoding explicitly. See Encodage de texte for more information.errors is an optional string that specifies how encoding and decoding errors are to be handled. Pass
'strict'
to raise aValueError
exception if there is an encoding error (the default ofNone
has the same effect), or pass'ignore'
to ignore errors. (Note that ignoring encoding errors can lead to data loss.)'replace'
causes a replacement marker (such as'?'
) to be inserted where there is malformed data.'backslashreplace'
causes malformed data to be replaced by a backslashed escape sequence. When writing,'xmlcharrefreplace'
(replace with the appropriate XML character reference) or'namereplace'
(replace with\N{...}
escape sequences) can be used. Any other error handling name that has been registered withcodecs.register_error()
is also valid.newline controls how line endings are handled. It can be
None
,''
,'\n'
,'\r'
, and'\r\n'
. It works as follows:When reading input from the stream, 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 newline is''
, universal newlines mode is enabled, but line endings are returned to the caller untranslated. If newline 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.Lors de l'écriture, si newline est
None
, chaque'\n'
est remplacé par le séparateur de lignes par défaut du systèmeos.linesep
. Si newline est*
ou'\n'
aucun remplacent n'est effectué. Si newline est un autre caractère valide, chaque'\n'
sera remplacé par la chaîne donnée.
If line_buffering is
True
,flush()
is implied when a call to write contains a newline character or a carriage return.If write_through is
True
, calls towrite()
are guaranteed not to be buffered: any data written on theTextIOWrapper
object is immediately handled to its underlying binary buffer.Modifié dans la version 3.3: Le paramètre write_through a été ajouté.
Modifié dans la version 3.3: The default encoding is now
locale.getpreferredencoding(False)
instead oflocale.getpreferredencoding()
. Don't change temporary the locale encoding usinglocale.setlocale()
, use the current locale encoding instead of the user preferred encoding.Modifié dans la version 3.10: The encoding argument now supports the
"locale"
dummy encoding name.TextIOWrapper
provides these data attributes and methods in addition to those fromTextIOBase
andIOBase
:- line_buffering¶
Whether line buffering is enabled.
- write_through¶
Whether writes are passed immediately to the underlying binary buffer.
Nouveau dans la version 3.7.
- reconfigure(*, encoding=None, errors=None, newline=None, line_buffering=None, write_through=None)¶
Reconfigure this text stream using new settings for encoding, errors, newline, line_buffering and write_through.
Parameters not specified keep current settings, except
errors='strict'
is used when encoding is specified but errors is not specified.Il n'est pas possible de modifier l'encodage ou une nouvelle ligne si des données ont déjà été lues à partir du flux. En revanche, il est possible de modifier l'encodage après l'écriture.
Cette méthode effectue un nettoyage implicite du flux avant de définir les nouveaux paramètres.
Nouveau dans la version 3.7.
Modifié dans la version 3.11: La méthode prend en charge l'option
encoding="locale"
.
- seek(cookie, whence=os.SEEK_SET, /)¶
Set the stream position. Return the new stream position as an
int
.Four operations are supported, given by the following argument combinations:
seek(0, SEEK_SET)
: Rewind to the start of the stream.seek(cookie, SEEK_SET)
: Restore a previous position; cookie must be a number returned bytell()
.seek(0, SEEK_END)
: Fast-forward to the end of the stream.seek(0, SEEK_CUR)
: Leave the current stream position unchanged.
Any other argument combinations are invalid, and may raise exceptions.
Voir aussi
os.SEEK_SET
,os.SEEK_CUR
, andos.SEEK_END
.
- class io.StringIO(initial_value='', newline='\n')¶
A text stream using an in-memory text buffer. It inherits from
TextIOBase
.The text buffer is discarded when the
close()
method is called.The initial value of the buffer can be set by providing initial_value. If newline translation is enabled, newlines will be encoded as if by
write()
. The stream is positioned at the start of the buffer which emulates opening an existing file in aw+
mode, making it ready for an immediate write from the beginning or for a write that would overwrite the initial value. To emulate opening a file in ana+
mode ready for appending, usef.seek(0, io.SEEK_END)
to reposition the stream at the end of the buffer.The newline argument works like that of
TextIOWrapper
, except that when writing output to the stream, if newline isNone
, newlines are written as\n
on all platforms.StringIO
provides this method in addition to those fromTextIOBase
andIOBase
:- getvalue()¶
Return a
str
containing the entire contents of the buffer. Newlines are decoded as if byread()
, although the stream position is not changed.
Exemple d'utilisation :
import io output = io.StringIO() output.write('First line.\n') print('Second line.', file=output) # Retrieve file contents -- this will be # 'First line.\nSecond line.\n' contents = output.getvalue() # Close object and discard memory buffer -- # .getvalue() will now raise an exception. output.close()
- class io.IncrementalNewlineDecoder¶
A helper codec that decodes newlines for universal newlines mode. It inherits from
codecs.IncrementalDecoder
.
Performances¶
Cette section aborde les performances des implémentations concrètes d'Entrée/Sortie fournies.
Binary I/O¶
By reading and writing only large chunks of data even when the user asks for a single byte, buffered I/O hides any inefficiency in calling and executing the operating system's unbuffered I/O routines. The gain depends on the OS and the kind of I/O which is performed. For example, on some modern OSes such as Linux, unbuffered disk I/O can be as fast as buffered I/O. The bottom line, however, is that buffered I/O offers predictable performance regardless of the platform and the backing device. Therefore, it is almost always preferable to use buffered I/O rather than unbuffered I/O for binary data.
Entrée/sortie de texte¶
Text I/O over a binary storage (such as a file) is significantly slower than
binary I/O over the same storage, because it requires conversions between
unicode and binary data using a character codec. This can become noticeable
handling huge amounts of text data like large log files. Also,
tell()
and seek()
are both quite slow
due to the reconstruction algorithm used.
StringIO
, however, is a native in-memory unicode container and will
exhibit similar speed to BytesIO
.
Fils d'exécution¶
FileIO
objects are thread-safe to the extent that the operating system
calls (such as read(2) under Unix) they wrap are thread-safe too.
Binary buffered objects (instances of BufferedReader
,
BufferedWriter
, BufferedRandom
and BufferedRWPair
)
protect their internal structures using a lock; it is therefore safe to call
them from multiple threads at once.
les objets TextIOWrapper
ne sont pas compatibles avec les programmes à fils d'exécutions multiples.
Réentrance¶
Binary buffered objects (instances of BufferedReader
,
BufferedWriter
, BufferedRandom
and BufferedRWPair
)
are not reentrant. While reentrant calls will not happen in normal situations,
they can arise from doing I/O in a signal
handler. If a thread tries to
re-enter a buffered object which it is already accessing, a RuntimeError
is raised. Note this doesn't prohibit a different thread from entering the
buffered object.
The above implicitly extends to text files, since the open()
function
will wrap a buffered object inside a TextIOWrapper
. This includes
standard streams and therefore affects the built-in print()
function as
well.