"compression.zstd" --- Compression compatible with the Zstandard format
***********************************************************************

Added in version 3.14.

**Source code:** 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.

The "compression.zstd" module contains:

* The "open()" function and "ZstdFile" class for reading and writing
  compressed files.

* The "ZstdCompressor" and "ZstdDecompressor" classes for incremental
  (de)compression.

* 一度に圧縮・展開を行う "compress()" および "decompress()" 関数。

* The "train_dict()" and "finalize_dict()" functions and the
  "ZstdDict" class to train and manage Zstandard dictionaries.

* The "CompressionParameter", "DecompressionParameter", and "Strategy"
  classes for setting advanced (de)compression parameters.

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 オプ
ションのモジュールの要件.


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.


圧縮ファイルへの読み書き
========================

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.

   以下のメソッドと属性も提供されています:

   peek(size=-1)

      ファイル上の現在位置を変更せずにバッファのデータを返します。EOF
      に達しない限り、少なくとも 1 バイトが返されます。返される正確な
      バイト数は規定されていません (引数 *size* は無視されます)。

      注釈:

        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'" は読み込み用、 "'wb'" は書き込み用です。

   name

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


メモリ上での圧縮と展開
======================

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)

   データをインクリメンタルに圧縮する圧縮オブジェクトを作成します。

   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)

      圧縮処理を終了し、コンプレッサの内部バッファにあるあらゆるデータ
      を格納する "bytes" オブジェクトを返します。

      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)

   データをインクリメンタルに展開するために使用できる展開オブジェクト
   を作成します。

   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.

   注釈:

     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 "ZstdDecompressor" instances.

   decompress(data, max_length=-1)

      Decompress *data* (a *bytes-like object*), returning
      uncompressed data as bytes. Some of *data* may be buffered
      internally, for use in later calls to "decompress()". The
      returned data should be concatenated with the output of any
      previous calls to "decompress()".

      If *max_length* is non-negative, the method returns at most
      *max_length* bytes of decompressed data. If this limit is
      reached and further output can be produced, the "needs_input"
      attribute will be set to "False". In this case, the next call to
      "decompress()" may provide *data* as "b''" to obtain more of the
      output.

      入力データの全てが圧縮され返された (*max_length* バイトより少な
      いためか *max_length* が負のため) 場合、 "needs_input" 属性は
      "True" になります。

      Attempting to decompress data after the end of a frame will
      raise a "ZstdError". Any data found after the end of the frame
      is ignored and saved in the "unused_data" attribute.

   eof

      ストリーム終端記号に到達した場合 "True" を返します。

   unused_data

      圧縮ストリームの末尾以降に存在したデータを表します。

      Before the end of the stream is reached, this will be "b''".

   needs_input

      "False" if the "decompress()" method can provide more
      decompressed data before requiring new compressed input.


Zstandard dictionaries
======================

compression.zstd.train_dict(samples, dict_size)

   Train a Zstandard dictionary, returning a "ZstdDict" instance.
   Zstandard dictionaries enable more efficient compression of smaller
   sizes of data, which is traditionally difficult to compress due to
   less repetition. If you are compressing multiple similar groups of
   data (such as similar files), Zstandard dictionaries can improve
   compression ratios and speed significantly.

   The *samples* argument (an iterable of "bytes" objects), is the
   population of samples used to train the Zstandard dictionary.

   The *dict_size* argument, an integer, is the maximum size (in
   bytes) the Zstandard dictionary should be. The Zstandard
   documentation suggests an absolute maximum of no more than 100 KB,
   but the maximum can often be smaller depending on the data. Larger
   dictionaries generally slow down compression, but improve
   compression ratios. Smaller dictionaries lead to faster
   compression, but reduce the compression ratio.

compression.zstd.finalize_dict(zstd_dict, /, samples, dict_size, level)

   An advanced function for converting a "raw content" Zstandard
   dictionary into a regular Zstandard dictionary. "Raw content"
   dictionaries are a sequence of bytes that do not need to follow the
   structure of a normal Zstandard dictionary.

   The *zstd_dict* argument is a "ZstdDict" instance with the
   "dict_content" containing the raw dictionary contents.

   The *samples* argument (an iterable of "bytes" objects), contains
   sample data for generating the Zstandard dictionary.

   The *dict_size* argument, an integer, is the maximum size (in
   bytes) the Zstandard dictionary should be. See "train_dict()" for
   suggestions on the maximum dictionary size.

   The *level* argument (an integer) is the compression level expected
   to be passed to the compressors using this dictionary. The
   dictionary information varies for each compression level, so tuning
   for the proper compression level can make compression more
   efficient.

class compression.zstd.ZstdDict(dict_content, /, *, is_raw=False)

   A wrapper around Zstandard dictionaries. Dictionaries can be used
   to improve the compression of many small chunks of data. Use
   "train_dict()" if you need to train a new dictionary from sample
   data.

   The *dict_content* argument (a *bytes-like object*), is the already
   trained dictionary information.

   The *is_raw* argument, a boolean, is an advanced parameter
   controlling the meaning of *dict_content*. "True" means
   *dict_content* is a "raw content" dictionary, without any format
   restrictions. "False" means *dict_content* is an ordinary Zstandard
   dictionary, created from Zstandard functions, for example,
   "train_dict()" or the external **zstd** CLI.

   When passing a "ZstdDict" to a function, the "as_digested_dict" and
   "as_undigested_dict" attributes can control how the dictionary is
   loaded by passing them as the "zstd_dict" argument, for example,
   "compress(data, zstd_dict=zd.as_digested_dict)". Digesting a
   dictionary is a costly operation that occurs when loading a
   Zstandard dictionary. When making multiple calls to compression or
   decompression, passing a digested dictionary will reduce the
   overhead of loading the dictionary.


      Difference for compression
      ^^^^^^^^^^^^^^^^^^^^^^^^^^

      +------------+----------------+------------+
      |            | Digested       | Undigested |
      |            | dictionary     | dictionary |
      |============|================|============|
      | Advanced   | "window_log",  | None       |
      | parameters | "hash_log",    |            |
      | of the     | "chain_log",   |            |
      | compressor | "search_log",  |            |
      | which may  | "min_match",   |            |
      | be         | "target_lengt  |            |
      | overridden | h",            |            |
      | by the di  | "strategy", "  |            |
      | ctionary's | enable_long_d  |            |
      | parameters | istance_match  |            |
      |            | ing", "ldm_ha  |            |
      |            | sh_log", "ldm  |            |
      |            | _min_match",   |            |
      |            | "ldm_bucket_s  |            |
      |            | ize_log", "ld  |            |
      |            | m_hash_rate_l  |            |
      |            | og", and some  |            |
      |            | non-public     |            |
      |            | parameters.    |            |
      +------------+----------------+------------+
      | "ZstdDict" | Yes. It's      | No. If you |
      | internally | faster when    | wish to    |
      | caches the | loading a      | load an    |
      | dictionary | digested       | undigested |
      |            | dictionary     | dictionary |
      |            | again with the | multiple   |
      |            | same           | times,     |
      |            | compression    | consider   |
      |            | level.         | reusing a  |
      |            |                | compressor |
      |            |                | object.    |
      +------------+----------------+------------+

   If passing a "ZstdDict" without any attribute, an undigested
   dictionary is passed by default when compressing and a digested
   dictionary is generated if necessary and passed by default when
   decompressing.

      dict_content

         The content of the Zstandard dictionary, a "bytes" object.
         It's the same as the *dict_content* argument in the
         "__init__" method. It can be used with other programs, such
         as the "zstd" CLI program.

      dict_id

         Identifier of the Zstandard dictionary, a non-negative int
         value.

         Non-zero means the dictionary is ordinary, created by
         Zstandard functions and following the Zstandard format.

         "0" means a "raw content" dictionary, free of any format
         restriction, used for advanced users.

         注釈:

           The meaning of "0" for "ZstdDict.dict_id" is different from
           the "dictionary_id" attribute to the "get_frame_info()"
           function.

      as_digested_dict

         Load as a digested dictionary.

      as_undigested_dict

         Load as an undigested dictionary.


Advanced parameter control
==========================

class compression.zstd.CompressionParameter

   An "IntEnum" containing the advanced compression parameter keys
   that can be used when compressing data.

   The "bounds()" method can be used on any attribute to get the valid
   values for that parameter.

   Parameters are optional; any omitted parameter will have it's value
   selected automatically.

   Example getting the lower and upper bound of "compression_level":

      lower, upper = CompressionParameter.compression_level.bounds()

   Example setting the "window_log" to the maximum size:

      _lower, upper = CompressionParameter.window_log.bounds()
      options = {CompressionParameter.window_log: upper}
      compress(b'venezuelan beaver cheese', options=options)

   bounds()

      Return the tuple of int bounds, "(lower, upper)", of a
      compression parameter. This method should be called on the
      attribute you wish to retrieve the bounds of. For example, to
      get the valid values for "compression_level", one may check the
      result of "CompressionParameter.compression_level.bounds()".

      Both the lower and upper bounds are inclusive.

   compression_level

      A high-level means of setting other compression parameters that
      affect the speed and ratio of compressing data.

      Regular compression levels are greater than "0". Values greater
      than "20" are considered "ultra" compression and require more
      memory than other levels. Negative values can be used to trade
      off faster compression for worse compression ratios.

      Setting the level to zero uses "COMPRESSION_LEVEL_DEFAULT".

   window_log

      Maximum allowed back-reference distance the compressor can use
      when compressing data, expressed as power of two, "1 <<
      window_log" bytes. This parameter greatly influences the memory
      usage of compression. Higher values require more memory but gain
      better compression values.

      A value of zero causes the value to be selected automatically.

   hash_log

      Size of the initial probe table, as a power of two. The
      resulting memory usage is "1 << (hash_log+2)" bytes. Larger
      tables improve compression ratio of strategies <= "dfast", and
      improve compression speed of strategies > "dfast".

      A value of zero causes the value to be selected automatically.

   chain_log

      Size of the multi-probe search table, as a power of two. The
      resulting memory usage is "1 << (chain_log+2)" bytes. Larger
      tables result in better and slower compression. This parameter
      has no effect for the "fast" strategy. It's still useful when
      using "dfast" strategy, in which case it defines a secondary
      probe table.

      A value of zero causes the value to be selected automatically.

   search_log

      Number of search attempts, as a power of two. More attempts
      result in better and slower compression. This parameter is
      useless for "fast" and "dfast" strategies.

      A value of zero causes the value to be selected automatically.

   min_match

      Minimum size of searched matches. Larger values increase
      compression and decompression speed, but decrease ratio. Note
      that Zstandard can still find matches of smaller size, it just
      tweaks its search algorithm to look for this size and larger.
      For all strategies < "btopt", the effective minimum is "4"; for
      all strategies > "fast", the effective maximum is "6".

      A value of zero causes the value to be selected automatically.

   target_length

      The impact of this field depends on the selected "Strategy".

      For strategies "btopt", "btultra" and "btultra2", the value is
      the length of a match considered "good enough" to stop
      searching. Larger values make compression ratios better, but
      compresses slower.

      For strategy "fast", it is the distance between match sampling.
      Larger values make compression faster, but with a worse
      compression ratio.

      A value of zero causes the value to be selected automatically.

   strategy

      The higher the value of selected strategy, the more complex the
      compression technique used by zstd, resulting in higher
      compression ratios but slower compression.

      参考: "Strategy"

   enable_long_distance_matching

      Long distance matching can be used to improve compression for
      large inputs by finding large matches at greater distances. It
      increases memory usage and window size.

      "True" or "1" enable long distance matching while "False" or "0"
      disable it.

      Enabling this parameter increases default "window_log" to 128
      MiB except when expressly set to a different value. This setting
      is enabled by default if "window_log" >= 128 MiB and the
      compression strategy >= "btopt" (compression level 16+).

   ldm_hash_log

      Size of the table for long distance matching, as a power of two.
      Larger values increase memory usage and compression ratio, but
      decrease compression speed.

      A value of zero causes the value to be selected automatically.

   ldm_min_match

      Minimum match size for long distance matcher. Larger or too
      small values can often decrease the compression ratio.

      A value of zero causes the value to be selected automatically.

   ldm_bucket_size_log

      Log size of each bucket in the long distance matcher hash table
      for collision resolution. Larger values improve collision
      resolution but decrease compression speed.

      A value of zero causes the value to be selected automatically.

   ldm_hash_rate_log

      Frequency of inserting/looking up entries into the long distance
      matcher hash table. Larger values improve compression speed.
      Deviating far from the default value will likely result in a
      compression ratio decrease.

      A value of zero causes the value to be selected automatically.

   content_size_flag

      Write the size of the data to be compressed into the Zstandard
      frame header when known prior to compressing.

      This flag only takes effect under the following scenarios:

      * Calling "compress()" for one-shot compression

      * Providing all of the data to be compressed in the frame in a
        single "ZstdCompressor.compress()" call, with the
        "ZstdCompressor.FLUSH_FRAME" mode.

      * Calling "ZstdCompressor.set_pledged_input_size()" with the
        exact amount of data that will be provided to the compressor
        prior to any calls to "ZstdCompressor.compress()" for the
        current frame. "ZstdCompressor.set_pledged_input_size()" must
        be called for each new frame.

      All other compression calls may not write the size information
      into the frame header.

      "True" or "1" enable the content size flag while "False" or "0"
      disable it.

   checksum_flag

      A four-byte checksum using XXHash64 of the uncompressed content
      is written at the end of each frame. Zstandard's decompression
      code verifies the checksum. If there is a mismatch a "ZstdError"
      exception is raised.

      "True" or "1" enable checksum generation while "False" or "0"
      disable it.

   dict_id_flag

      When compressing with a "ZstdDict", the dictionary's ID is
      written into the frame header.

      "True" or "1" enable storing the dictionary ID while "False" or
      "0" disable it.

   nb_workers

      Select how many threads will be spawned to compress in parallel.
      When "nb_workers" > 0, enables multi-threaded compression, a
      value of "1" means "one-thread multi-threaded mode". More
      workers improve speed, but also increase memory usage and
      slightly reduce compression ratio.

      A value of zero disables multi-threading.

   job_size

      Size of a compression job, in bytes. This value is enforced only
      when "nb_workers" >= 1. Each compression job is completed in
      parallel, so this value can indirectly impact the number of
      active threads.

      A value of zero causes the value to be selected automatically.

   overlap_log

      Sets how much data is reloaded from previous jobs (threads) for
      new jobs to be used by the look behind window during
      compression. This value is only used when "nb_workers" >= 1.
      Acceptable values vary from 0 to 9.

         * 0 means dynamically set the overlap amount

         * 1 means no overlap

         * 9 means use a full window size from the previous job

      Each increment halves/doubles the overlap size. "8" means an
      overlap of "window_size/2", "7" means an overlap of
      "window_size/4", etc.

class compression.zstd.DecompressionParameter

   An "IntEnum" containing the advanced decompression parameter keys
   that can be used when decompressing data. Parameters are optional;
   any omitted parameter will have it's value selected automatically.

   The "bounds()" method can be used on any attribute to get the valid
   values for that parameter.

   Example setting the "window_log_max" to the maximum size:

      data = compress(b'Some very long buffer of bytes...')

      _lower, upper = DecompressionParameter.window_log_max.bounds()

      options = {DecompressionParameter.window_log_max: upper}
      decompress(data, options=options)

   bounds()

      Return the tuple of int bounds, "(lower, upper)", of a
      decompression parameter. This method should be called on the
      attribute you wish to retrieve the bounds of.

      Both the lower and upper bounds are inclusive.

   window_log_max

      The base-two logarithm of the maximum size of the window used
      during decompression. This can be useful to limit the amount of
      memory used when decompressing data. A larger maximum window
      size leads to faster decompression.

      A value of zero causes the value to be selected automatically.

class compression.zstd.Strategy

   An "IntEnum" containing strategies for compression. Higher-numbered
   strategies correspond to more complex and slower compression.

   注釈:

     The values of attributes of "Strategy" are not necessarily stable
     across zstd versions. Only the ordering of the attributes may be
     relied upon. The attributes are listed below in order.

   The following strategies are available:

   fast

   dfast

   greedy

   lazy

   lazy2

   btlazy2

   btopt

   btultra

   btultra2


その他
======

compression.zstd.get_frame_info(frame_buffer)

   Retrieve a "FrameInfo" object containing metadata about a Zstandard
   frame. Frames contain metadata related to the compressed data they
   hold.

class compression.zstd.FrameInfo

   Metadata related to a Zstandard frame.

   decompressed_size

      The size of the decompressed contents of the frame.

   dictionary_id

      An integer representing the Zstandard dictionary ID needed for
      decompressing the frame. "0" means the dictionary ID was not
      recorded in the frame header. This may mean that a Zstandard
      dictionary is not needed, or that the ID of a required
      dictionary was not recorded.

compression.zstd.COMPRESSION_LEVEL_DEFAULT

   The default compression level for Zstandard: "3".

compression.zstd.zstd_version_info

   Version number of the runtime zstd library as a tuple of integers
   (major, minor, release).


使用例
======

Reading in a compressed file:

   from compression import zstd

   with zstd.open("file.zst") as f:
       file_content = f.read()

Creating a compressed file:

   from compression import zstd

   data = b"Insert Data Here"
   with zstd.open("file.zst", "w") as f:
       f.write(data)

Compressing data in memory:

   from compression import zstd

   data_in = b"Insert Data Here"
   data_out = zstd.compress(data_in)

Incremental compression:

   from compression import zstd

   comp = zstd.ZstdCompressor()
   out1 = comp.compress(b"Some data\n")
   out2 = comp.compress(b"Another piece of data\n")
   out3 = comp.compress(b"Even more data\n")
   out4 = comp.flush()
   # Concatenate all the partial results:
   result = b"".join([out1, out2, out3, out4])

Writing compressed data to an already-open file:

   from compression import zstd

   with open("myfile", "wb") as f:
       f.write(b"This data will not be compressed\n")
       with zstd.open(f, "w") as zstf:
           zstf.write(b"This *will* be compressed\n")
       f.write(b"Not compressed\n")

Creating a compressed file using compression parameters:

   from compression import zstd

   options = {
      zstd.CompressionParameter.checksum_flag: 1
   }
   with zstd.open("file.zst", "w", options=options) as f:
       f.write(b"Mind if I squeeze in?")
