compression.zstd --- 與 Zstandard 格式相容的壓縮

在 3.14 版被加入.

原始碼：Lib/compression/zstd/__init__.py

This module provides classes and functions for compressing and decompressing data using the Zstandard (or zstd) compression algorithm. The zstd manual describes Zstandard as "a fast lossless compression algorithm, targeting real-time compression scenarios at zlib-level and better compression ratios." Also included is a file interface that supports reading and writing the contents of .zst files created by the zstd utility, as well as raw zstd compressed streams.

compression.zstd 模組包含：

This is an optional module. If it is missing from your copy of CPython, look for documentation from your distributor (that is, whoever provided Python to you). If you are the distributor, see 可選模組的需求.

例外

exception compression.zstd.ZstdError

This exception is raised when an error occurs during compression or decompression, or while initializing the (de)compressor state.

Reading and writing compressed files

compression.zstd.open(file, /, mode='rb', *, level=None, options=None, zstd_dict=None, encoding=None, errors=None, newline=None)

Open a Zstandard-compressed file in binary or text mode, returning a file object.

The file argument can be either a file name (given as a str, bytes or path-like object), in which case the named file is opened, or it can be an existing file object to read from or write to.

The mode argument can be either 'rb' for reading (default), 'wb' for overwriting, 'ab' for appending, or 'xb' for exclusive creation. These can equivalently be given as 'r', 'w', 'a', and 'x' respectively. You may also open in text mode with 'rt', 'wt', 'at', and 'xt' respectively.

When reading, the options argument can be a dictionary providing advanced decompression parameters; see DecompressionParameter for detailed information about supported parameters. The zstd_dict argument is a ZstdDict instance to be used during decompression. When reading, if the level argument is not None, a TypeError will be raised.

When writing, the options argument can be a dictionary providing advanced compression parameters; see CompressionParameter for detailed information about supported parameters. The level argument is the compression level to use when writing compressed data. Only one of level or options may be non-None. The zstd_dict argument is a ZstdDict instance to be used during compression.

In binary mode, this function is equivalent to the ZstdFile constructor: ZstdFile(file, mode, ...). In this case, the encoding, errors, and newline parameters must not be provided.

In text mode, a ZstdFile object is created, and wrapped in an io.TextIOWrapper instance with the specified encoding, error handling behavior, and line endings.

class compression.zstd.ZstdFile(file, /, mode='rb', *, level=None, options=None, zstd_dict=None)

Open a Zstandard-compressed file in binary mode.

A ZstdFile can wrap an already-open file object, or operate directly on a named file. The file argument specifies either the file object to wrap, or the name of the file to open (as a str, bytes or path-like object). If wrapping an existing file object, the wrapped file will not be closed when the ZstdFile is closed.

The mode argument can be either 'rb' for reading (default), 'wb' for overwriting, 'xb' for exclusive creation, or 'ab' for appending. These can equivalently be given as 'r', 'w', 'x' and 'a' respectively.

If file is a file object (rather than an actual file name), a mode of 'w' does not truncate the file, and is instead equivalent to 'a'.

When reading, the options argument can be a dictionary providing advanced decompression parameters; see DecompressionParameter for detailed information about supported parameters. The zstd_dict argument is a ZstdDict instance to be used during decompression. When reading, if the level argument is not None, a TypeError will be raised.

When writing, the options argument can be a dictionary providing advanced compression parameters; see CompressionParameter for detailed information about supported parameters. The level argument is the compression level to use when writing compressed data. Only one of level or options may be passed. The zstd_dict argument is a ZstdDict instance to be used during compression.

ZstdFile supports all the members specified by io.BufferedIOBase, except for detach() and truncate(). Iteration and the with statement are supported.

The following method and attributes are also provided:

peek(size=-1)

Return buffered data without advancing the file position. At least one byte of data will be returned, unless EOF has been reached. The exact number of bytes returned is unspecified (the size argument is ignored).

備註

While calling peek() does not change the file position of the ZstdFile, it may change the position of the underlying file object (for example, if the ZstdFile was constructed by passing a file object for file).

mode

'rb' for reading and 'wb' for writing.

name

The name of the Zstandard file. Equivalent to the name attribute of the underlying file object.

Compressing and decompressing data in memory

compression.zstd.compress(data, level=None, options=None, zstd_dict=None)

Compress data (a bytes-like object), returning the compressed data as a bytes object.

The level argument is an integer controlling the level of compression. level is an alternative to setting CompressionParameter.compression_level in options. Use bounds() on compression_level to get the values that can be passed for level. If advanced compression options are needed, the level argument must be omitted and in the options dictionary the CompressionParameter.compression_level parameter should be set.

The options argument is a Python dictionary containing advanced compression parameters. The valid keys and values for compression parameters are documented as part of the CompressionParameter documentation.

The zstd_dict argument is an instance of ZstdDict containing trained data to improve compression efficiency. The function train_dict() can be used to generate a Zstandard dictionary.

compression.zstd.decompress(data, zstd_dict=None, options=None)

Decompress data (a bytes-like object), returning the uncompressed data as a bytes object.

The options argument is a Python dictionary containing advanced decompression parameters. The valid keys and values for compression parameters are documented as part of the DecompressionParameter documentation.

The zstd_dict argument is an instance of ZstdDict containing trained data used during compression. This must be the same Zstandard dictionary used during compression.

If data is the concatenation of multiple distinct compressed frames, decompress all of these frames, and return the concatenation of the results.

class compression.zstd.ZstdCompressor(level=None, options=None, zstd_dict=None)

Create a compressor object, which can be used to compress data incrementally.

For a more convenient way of compressing a single chunk of data, see the module-level function compress().

The level argument is an integer controlling the level of compression. level is an alternative to setting CompressionParameter.compression_level in options. Use bounds() on compression_level to get the values that can be passed for level. If advanced compression options are needed, the level argument must be omitted and in the options dictionary the CompressionParameter.compression_level parameter should be set.

The options argument is a Python dictionary containing advanced compression parameters. The valid keys and values for compression parameters are documented as part of the CompressionParameter documentation.

The zstd_dict argument is an optional instance of ZstdDict containing trained data to improve compression efficiency. The function train_dict() can be used to generate a Zstandard dictionary.

compress(data, mode=ZstdCompressor.CONTINUE)

Compress data (a bytes-like object), returning a bytes object with compressed data if possible, or otherwise an empty bytes object. Some of data may be buffered internally, for use in later calls to compress() and flush(). The returned data should be concatenated with the output of any previous calls to compress().

The mode argument is a ZstdCompressor attribute, either CONTINUE, FLUSH_BLOCK, or FLUSH_FRAME.

When all data has been provided to the compressor, call the flush() method to finish the compression process. If compress() is called with mode set to FLUSH_FRAME, flush() should not be called, as it would write out a new empty frame.

flush(mode=ZstdCompressor.FLUSH_FRAME)

Finish the compression process, returning a bytes object containing any data stored in the compressor's internal buffers.

The mode argument is a ZstdCompressor attribute, either FLUSH_BLOCK, or FLUSH_FRAME.

set_pledged_input_size(size)

Specify the amount of uncompressed data size that will be provided for the next frame. size will be written into the frame header of the next frame unless CompressionParameter.content_size_flag is False or 0. A size of 0 means that the frame is empty. If size is None, the frame header will omit the frame size. Frames that include the uncompressed data size require less memory to decompress, especially at higher compression levels.

If last_mode is not FLUSH_FRAME, a ValueError is raised as the compressor is not at the start of a frame. If the pledged size does not match the actual size of data provided to compress(), future calls to compress() or flush() may raise ZstdError and the last chunk of data may be lost.

After flush() or compress() are called with mode FLUSH_FRAME, the next frame will not include the frame size into the header unless set_pledged_input_size() is called again.

CONTINUE

Collect more data for compression, which may or may not generate output immediately. This mode optimizes the compression ratio by maximizing the amount of data per block and frame.

FLUSH_BLOCK

Complete and write a block to the data stream. The data returned so far can be immediately decompressed. Past data can still be referenced in future blocks generated by calls to compress(), improving compression.

FLUSH_FRAME

Complete and write out a frame. Future data provided to compress() will be written into a new frame and cannot reference past data.

last_mode

The last mode passed to either compress() or flush(). The value can be one of CONTINUE, FLUSH_BLOCK, or FLUSH_FRAME. The initial value is FLUSH_FRAME, signifying that the compressor is at the start of a new frame.

class compression.zstd.ZstdDecompressor(zstd_dict=None, options=None)

Create a decompressor object, which can be used to decompress data incrementally.

For a more convenient way of decompressing an entire compressed stream at once, see the module-level function decompress().

The options argument is a Python dictionary containing advanced decompression parameters. The valid keys and values for compression parameters are documented as part of the DecompressionParameter documentation.

The zstd_dict argument is an instance of ZstdDict containing trained data used during compression. This must be the same Zstandard dictionary used during compression.

備註

This class does not transparently handle inputs containing multiple compressed frames, unlike the decompress() function and ZstdFile class. To decompress a multi-frame input, you should use decompress(), ZstdFile if working with a file object, or multiple