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io — 用于操控流的核心工具

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`io` — 用于操控流的核心工具 ¶

源代码： Lib/io.py

概述 ¶

The io 模块为 Python 处理各种类型 I/O 提供主要设施。有 3 种主要 I/O 类型： 文本 I/O , 二进制 I/O and 原生 I/O 。这些是一般类别，且它们中的每个都可以用于各种后备存储。属于这些类别的任何具体对象称为文件对象。其它常见术语是 stream and 像文件对象 .

独立于类别，每个具体流对象还有各种能力：可以只读、只写或读写。还允许任意随机访问 (向前或向后寻址到任何位置) 或仅顺序访问 (例如：在套接字或管道情况下)。

所有流都关切赋予给它们的有关数据类型。例如，赋予 str 对象到 write() 方法对于二进制流将引发 TypeError 。同样，赋予 bytes 对象到 write() 方法对于文本流。

3.3 版改变：操作用于引发 IOError 现在引发 OSError ，由于 IOError 现在是别名化的 OSError .

文本 I/O ¶

Text I/O 期望并产生 str 对象。这意味着每当后备存储是本机字节 (譬如：在文件情况下) 时，数据的编码和解码是透明的，还能可选翻译特定平台换行符。

创建文本流的最轻松方式是采用 open() ，可选指定编码：

f = open("myfile.txt", "r", encoding="utf-8")

内存文本流还可用作 StringIO 对象：

f = io.StringIO("some initial text data")

文本流 API 的详细描述在文档编制 TextIOBase .

二进制 I/O ¶

二进制 I/O (也称 缓冲 I/O ) 期望像字节对象并产生 bytes 对象。不履行编码、解码或翻译换行符。这种类别的流可以用于所有种类的非文本数据，且当期望手动控制文本数据的处理时也如此。

创建二进制流的最简单方式是采用 open() with 'b' 在模式字符串下：

f = open("myfile.jpg", "rb")

内存二进制流还可用作 BytesIO 对象：

f = io.BytesIO(b"some initial binary data: \x00\x01")

二进制流 API 的详细描述在文档化的 BufferedIOBase .

其它库模块可以提供创建文本 (或二进制) 流的额外方式。见 socket.socket.makefile() 例如。

原生 I/O ¶

原生 I/O (也称 无缓冲 I/O ) 通常用作二进制和文本流的低级构建块；直接操纵来自用户代码的原生流很少有用。尽管如此，可以通过在禁用缓冲的二进制模式下打开文件，创建原生流：

f = open("myfile.jpg", "rb", buffering=0)

原生流 API 的详细描述在文档化的 RawIOBase .

文本编码 ¶

默认编码对于 TextIOWrapper and open() 是特定区域设置 ( 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.

另请参阅

Python UTF-8 模式: Python UTF-8 Mode can be used to change the default encoding to UTF-8 from locale-specific encoding.
PEP 686: Python 3.15 将使 Python UTF-8 模式默认。

选择加入 EncodingWarning ¶

Added in version 3.10: 见 PEP 597 了解更多细节。

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.

高级模块接口 ¶

io. DEFAULT_BUFFER_SIZE ¶: 包含用于模块缓冲 I/O 类的默认缓冲大小的 int。 open() 使用文件 blksize (如获得通过 os.stat() ) 若可能的话。

io. open ( file , mode = 'r' , buffering = -1 , encoding = None , errors = None , newline = None , closefd = True , opener = None ) ¶

这是别名化的内置 open() 函数。

此函数引发审计事件 open 采用自变量 path , mode and flags 。 mode and flags 自变量可能已被修改 (或推断自原始调用)。

io. open_code ( path ) ¶

打开提供文件按模式 'rb' 。应使用此函数，当意图将内容视为可执行代码时。

path 应该为 str 和绝对路径。

可能覆写此函数的行为由早期调用 PyFile_SetOpenCodeHook() 。不管怎样，假定 path 是 str 和绝对路径， open_code(path) 行为应始终如同 open(path, 'rb') 。覆写行为旨在额外验证 (或预处理) 文件。

Added in version 3.8.

io. text_encoding ( encoding , stacklevel = 2 , / ) ¶

这是帮手函数适于可调用使用 open() or TextIOWrapper 且拥有 encoding=None 参数。

此函数返回 encoding 若它不为 None 。否则，它返回 "locale" or "utf-8" 从属 UTF-8 模式 .

此函数发射 EncodingWarning if sys.flags.warn_default_encoding 为 True 和 encoding is None . stacklevel 指定在哪里发射警告。例如：

def read_text(path, encoding=None):
    encoding = io.text_encoding(encoding)  # stacklevel=2
    with open(path, encoding) as f:
        return f.read()

在此范例中， EncodingWarning 被发射对于调用者的 read_text() .

见文本编码了解更多信息。

Added in version 3.10.

3.11 版改变： text_encoding() 返回 utf-8 当 UTF-8 模式被启用且 encoding is None .

exception io. BlockingIOError ¶: 这是兼容性别名对于内置 BlockingIOError 异常。

exception io. UnsupportedOperation ¶: 异常继承 OSError and ValueError 这被引发，当在流上调用不支持操作时。

另请参阅

sys

类层次结构 ¶

I/O 流实现的组织是按类层次结构。首先抽象基类 (ABC) 用于指定流的各种类别，然后具体类提供标准流实现。

注意

ABC (抽象基类) 还提供了一些方法的默认实现，以帮助实现具体的流类。例如， BufferedIOBase 提供实现未优化的 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 若它们不支持给定操作。

The RawIOBase ABC (抽象基类) 延伸 IOBase . It deals with the reading and writing of bytes to a stream. FileIO 子类 RawIOBase to provide an interface to files in the machine’s file system.

The BufferedIOBase ABC (抽象基类) 延伸 IOBase . It deals with buffering on a raw binary stream ( RawIOBase )。其子类， BufferedWriter , BufferedReader ，和 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 子类， BytesIO , is a stream of in-memory bytes.

The TextIOBase ABC (抽象基类) 延伸 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 是用于文本的内存流。

Argument names are not part of the specification, and only the arguments of open() are intended to be used as keyword arguments.

下表汇总的 ABC (抽象基类) 提供通过 io 模块：

ABC (抽象基类)	继承	Stub 方法	混合方法和特性
`IOBase`		`fileno` , `seek` ，和 `truncate`	`close` , `closed` , `__enter__` , `__exit__` , `flush` , `isatty` , `__iter__` , `__next__` , `readable` , `readline` , `readlines` , `seekable` , `tell` , `writable` ，和 `writelines`
`RawIOBase`	`IOBase`	`readinto` and `write`	继承 `IOBase` 方法， `read` ，和 `readall`
`BufferedIOBase`	`IOBase`	`detach` , `read` , `read1` ，和 `write`	继承 `IOBase` 方法， `readinto` ，和 `readinto1`
`TextIOBase`	`IOBase`	`detach` , `read` , `readline` ，和 `write`	继承 `IOBase` 方法， `encoding` , `errors` ，和 `newlines`

I/O 基类 ¶

class io. IOBase ¶

class io. RawIOBase ¶

class io. BufferedIOBase ¶

原生文件 I/O ¶

class io. FileIO ( name , mode = 'r' , closefd = True , opener = None ) ¶

class io. BufferedReader ( raw , buffer_size = DEFAULT_BUFFER_SIZE ) ¶

class io. BufferedWriter ( raw , buffer_size = DEFAULT_BUFFER_SIZE ) ¶

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 from BufferedReader and BufferedWriter .

The constructor creates a reader and writer for a seekable raw stream, given in the first argument. If the buffer_size is omitted it defaults to DEFAULT_BUFFER_SIZE .

BufferedRandom is capable of anything BufferedReader or BufferedWriter can do. In addition, seek() and tell() 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 from BufferedIOBase .

reader and writer are RawIOBase objects that are readable and writeable respectively. If the buffer_size is omitted it defaults to DEFAULT_BUFFER_SIZE .

BufferedRWPair 实现所有的 BufferedIOBase 方法除了 detach() ，其引发 UnsupportedOperation .

警告

BufferedRWPair does not attempt to synchronize accesses to its underlying raw streams. You should not pass it the same object as reader and writer; use BufferedRandom 代替。

文本 I/O ¶

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 提供 (或覆写) 了这些数据属性和方法，除了那些来自 IOBase :

encoding ¶: 用于将流字节解码成字符串，和将字符串编码成字节的编码名称。

errors ¶

newlines ¶

buffer ¶: 底层二进制缓冲 ( BufferedIOBase 实例) TextIOBase 的处理。这不属于 TextIOBase API 且在某些实现中可能不存在。

detach ( ) ¶

分隔底层二进制缓冲从 TextIOBase 并返回它。

分离底层缓冲后， TextIOBase 处于不可用状态。

某些 TextIOBase 实现，像 StringIO ，可能没有底层缓冲概念且调用此方法会引发 UnsupportedOperation .

Added in version 3.1.

read ( size = -1 , / ) ¶: 读取并返回最多 size 字符从流作为单 str 。若 size 为负或者 None ，读取直到 EOF (文件末尾)。

readline ( size = -1 , / ) ¶

读取直到换行符或 EOF (文件末尾) 并返回单 str 。若流已在 EOF (文件末尾)，返回空字符串。

若 size 有指定，最多 size 字符将被读取。

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 or 0 : seek from the start of the stream (the default); offset must either be a number returned by TextIOBase.tell() , or zero. Any other offset value produces undefined behaviour.
SEEK_CUR or 1 : “seek” to the current position; offset must be zero, which is a no-operation (all other values are unsupported).
SEEK_END or 2 : seek to the end of the stream; offset must be zero (all other values are unsupported).

以不透明数字形式返回新的绝对位置。

Added in version 3.1: The SEEK_* 常量。

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 , / ) ¶: 写入字符串 s 到流并返回写入字符数。

class io. TextIOWrapper ( buffer , encoding = None , errors = None , newline = None , line_buffering = False , write_through = False ) ¶

缓冲文本流提供更高级访问对 BufferedIOBase buffered binary stream. It inherits from TextIOBase .

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 文本编码了解更多信息。

errors is an optional string that specifies how encoding and decoding errors are to be handled. Pass 'strict' 会引发 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.) 'replace' 导致置换标记 (譬如 '?' ) 被插入在畸形数据处。 '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 with codecs.register_error() is also valid.

newline controls how line endings are handled. It can be None , '' , '\n' , '\r' ，和 '\r\n' 。其工作如下：

当从流读取输入时，若 newline is None , 通用换行符 mode is enabled. Lines in the input can end in '\n' , '\r' ，或 '\r\n' ，且这些会被翻译成 '\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.
当写入输出到流时，若 newline is None ，任何 '\n' 写入字符被翻译成系统默认行分隔符， os.linesep 。若 newline is '' or '\n' ，不发生翻译。若 newline 是任何其它合法值，任何 '\n' 写入字符被翻译成给定字符串。

若 line_buffering is True , flush() is implied when a call to write contains a newline character or a carriage return.

若 write_through is True ，调用 write() are guaranteed not to be buffered: any data written on the TextIOWrapper object is immediately handled to its underlying binary buffer .

3.3 版改变： The write_through 自变量被添加。

3.3 版改变：默认 encoding 现为 locale.getpreferredencoding(False) 而不是 locale.getpreferredencoding() . Don’t change temporary the locale encoding using locale.setlocale() , use the current locale encoding instead of the user preferred encoding.

3.10 版改变： The encoding 自变量现在支持 "locale" 虚设编码名称。

TextIOWrapper 提供这些数据属性和方法，除了那些来自 TextIOBase and IOBase :

line_buffering ¶: 行缓冲是否被启用。

write_through ¶

Whether writes are passed immediately to the underlying binary buffer.

Added in version 3.7.

reconfigure ( * , encoding = None , errors = None , newline = None , line_buffering = None , write_through = None ) ¶

重新配置此文本流使用新设置为 encoding , errors , newline , line_buffering and write_through .

未指定参数保持当前设置，除了 errors='strict' 的使用当 encoding 有指定但 errors 未指定。

改变 encoding 或 newline 不可能，若已从流读取了一些数据。另一方面，写入后改变 encoding 是可能的。

此方法做隐式流刷新，在设置新参数前。

Added in version 3.7.

3.11 版改变：方法支持 encoding="locale" 选项。

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 必须为 a number returned by tell() .
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.

另请参阅

os.SEEK_SET , os.SEEK_CUR ，和 os.SEEK_END .

tell ( ) ¶: Return the stream position as an opaque number. The return value of tell() can be given as input to seek() , to restore a previous stream position.

class io. StringIO ( initial_value = '' , newline = '\n' ) ¶

A text stream using an in-memory text buffer. It inherits from TextIOBase .

文本缓冲被丢弃当 close() 方法被调用。

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 a w+ 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 an a+ mode ready for appending, use f.seek(0, io.SEEK_END) to reposition the stream at the end of the buffer.

The newline 自变量的工作像 TextIOWrapper , except that when writing output to the stream, if newline is None , newlines are written as \n 在所有平台。

StringIO 提供此方法，除了那些来自 TextIOBase and IOBase :

getvalue ( ) ¶: 返回 str containing the entire contents of the buffer. Newlines are decoded as if by read() , although the stream position is not changed.

用法范例：

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 ¶: 解码换行符的帮手编解码器，对于通用换行符 mode. It inherits from codecs.IncrementalDecoder .

性能 ¶

本节讨论提供的具体 I/O 实现的性能。

二进制 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.

文本 I/O ¶

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 ，不管怎样，是本机内存 unicode 容器，且显露速度类似 BytesIO .

多线程 ¶

FileIO 对象在操作系统调用程度是线程安全的 (譬如 read(2) 在 Unix)，它们的包裹也是线程安全的。

二进制缓冲对象 (实例化的 BufferedReader , BufferedWriter , BufferedRandom and BufferedRWPair ) protect their internal structures using a lock; it is therefore safe to call them from multiple threads at once.

TextIOWrapper 对象不是线程安全的。

重入 ¶

二进制缓冲对象 (实例化的 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.