:mod:`!compression.zstd` --- Compression compatible with the Zstandard format

.. module:: compression.zstd :synopsis: Low-level interface to compression and decompression routines in the zstd library.

.. versionadded:: 3.14

Source code: :source: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 <https://facebook.github.io/zstd/doc/api_manual_latest.html>__ 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 :program:zstd utility, as well as raw zstd compressed streams.

The :mod:!compression.zstd module contains:

The :func:.open function and :class:ZstdFile class for reading and writing compressed files.
The :class:ZstdCompressor and :class:ZstdDecompressor classes for incremental (de)compression.
The :func:compress and :func:decompress functions for one-shot (de)compression.
The :func:train_dict and :func:finalize_dict functions and the :class:ZstdDict class to train and manage Zstandard dictionaries.
The :class:CompressionParameter, :class:DecompressionParameter, and :class:Strategy classes for setting advanced (de)compression parameters.

.. include:: ../includes/optional-module.rst

Exceptions

.. exception:: 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

.. function:: 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 :term:file object.

The file argument can be either a file name (given as a :class:str, :class:bytes or :term:path-like <path-like object> 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 :class:DecompressionParameter for detailed information about supported parameters. The zstd_dict argument is a :class:ZstdDict instance to be used during decompression. When reading, if the level argument is not None, a :exc:!TypeError will be raised.

When writing, the options argument can be a dictionary providing advanced compression parameters; see :class: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 :class:ZstdDict instance to be used during compression.

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

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

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

Open a Zstandard-compressed file in binary mode.

A :class:ZstdFile can wrap an already-open :term: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 :class:str, :class:bytes or :term:path-like <path-like object> object). If wrapping an existing file object, the wrapped file will not be closed when the :class: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 writing, the options argument can be a dictionary providing advanced compression parameters; see :class: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 :class:ZstdDict instance to be used during compression.

:class:!ZstdFile supports all the members specified by :class:io.BufferedIOBase, except for :meth:~io.BufferedIOBase.detach and :meth:~io.IOBase.truncate. Iteration and the :keyword:with statement are supported.

The following method and attributes are also provided:

.. method:: 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).

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

.. attribute:: mode

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

.. attribute:: name

  The name of the Zstandard file. Equivalent to the :attr:`~io.FileIO.name`
  attribute of the underlying :term:`file object`.

Compressing and decompressing data in memory

.. function:: compress(data, level=None, options=None, zstd_dict=None)

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

The level argument is an integer controlling the level of compression. level is an alternative to setting :attr:CompressionParameter.compression_level in options. Use :meth:~CompressionParameter.bounds on :attr:~CompressionParameter.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 :attr:!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 :class:CompressionParameter documentation.

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

.. function:: decompress(data, zstd_dict=None, options=None)

Decompress data (a :term:bytes-like object), returning the uncompressed data as a :class: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 :class:DecompressionParameter documentation.

The zstd_dict argument is an instance of :class: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:: 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 :func:compress.

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

.. method:: compress(data, mode=ZstdCompressor.CONTINUE)

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

  The *mode* argument is a :class:`ZstdCompressor` attribute, either
  :attr:`~.CONTINUE`, :attr:`~.FLUSH_BLOCK`,
  or :attr:`~.FLUSH_FRAME`.

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

.. method:: flush(mode=ZstdCompressor.FLUSH_FRAME)

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

  The *mode* argument is a :class:`ZstdCompressor` attribute, either
  :attr:`~.FLUSH_BLOCK`, or :attr:`~.FLUSH_FRAME`.

.. method:: 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 :attr:`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 :attr:`last_mode` is not :attr:`FLUSH_FRAME`, a
  :exc:`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 :meth:`.compress`, future calls to :meth:`!compress` or
  :meth:`flush` may raise :exc:`ZstdError` and the last chunk of data may
  be lost.

  After :meth:`flush` or :meth:`.compress` are called with mode
  :attr:`FLUSH_FRAME`, the next frame will not include the frame size into
  the header unless :meth:`!set_pledged_input_size` is called again.

.. attribute:: 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.

.. attribute:: 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 :meth:`~.compress`,
  improving compression.

.. attribute:: FLUSH_FRAME

  Complete and write out a frame. Future data provided to
  :meth:`~.compress` will be written into a new frame and
  *cannot* reference past data.

.. attribute:: last_mode

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

.. class:: 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 :func:decompress.

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

.. note:: This class does not transparently handle inputs containing multiple compressed frames, unlike the :func:decompress function and :class:ZstdFile class. To decompress a multi-frame input, you should use :func:decompress, :class:ZstdFile if working with a :term:file object, or multiple :class:!ZstdDecompressor instances.

.. method:: decompress(data, max_length=-1)

  Decompress *data* (a :term:`bytes-like object`), returning
  uncompressed data as bytes. Some of *data* may be buffered
  internally, for use in later calls to :meth:`!decompress`.
  The returned data should be concatenated with the output of any previous
  calls to :meth:`!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 :attr:`~.needs_input` attribute will
  be set to ``False``. In this case, the next call to
  :meth:`~.decompress` may provide *data* as ``b''`` to obtain
  more of the output.

  If all of the input data was decompressed and returned (either
  because this was less than *max_length* bytes, or because
  *max_length* was negative), the :attr:`~.needs_input` attribute
  will be set to ``True``.

  Attempting to decompress data after the end of a frame will raise a
  :exc:`ZstdError`. Any data found after the end of the frame is ignored
  and saved in the :attr:`~.unused_data` attribute.

.. attribute:: eof

  ``True`` if the end-of-stream marker has been reached.

.. attribute:: unused_data

  Data found after the end of the compressed stream.

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

.. attribute:: needs_input

  ``False`` if the :meth:`.decompress` method can provide more
  decompressed data before requiring new compressed input.

Zstandard dictionaries

.. function:: train_dict(samples, dict_size)

Train a Zstandard dictionary, returning a :class: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 :class: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.

.. function:: 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 :class:ZstdDict instance with the :attr:~ZstdDict.dict_content containing the raw dictionary contents.

The samples argument (an iterable of :class: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 :func: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:: 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 :func:train_dict if you need to train a new dictionary from sample data.

The dict_content argument (a :term: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, :func:train_dict or the external :program:zstd CLI.

When passing a :class:!ZstdDict to a function, the :attr:!as_digested_dict and :attr:!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.

.. list-table:: Difference for compression
   :widths: 10 14 10
   :header-rows: 1

   * -
     - Digested dictionary
     - Undigested dictionary
   * - Advanced parameters of the compressor which may be overridden by
       the dictionary's parameters
     - ``window_log``, ``hash_log``, ``chain_log``, ``search_log``,
       ``min_match``, ``target_length``, ``strategy``,
       ``enable_long_distance_matching``, ``ldm_hash_log``,
       ``ldm_min_match``, ``ldm_bucket_size_log``, ``ldm_hash_rate_log``,
       and some non-public parameters.
     - None
   * - :class:`!ZstdDict` internally caches the dictionary
     - Yes. It's faster when loading a digested dictionary again with the
       same compression level.
     - No. If you wish to load an undigested dictionary multiple times,
       consider reusing a compressor object.

If passing a :class:!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.

.. attribute:: 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.

.. attribute:: 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.

    .. note::

        The meaning of ``0`` for :attr:`!ZstdDict.dict_id` is different
        from the ``dictionary_id`` attribute to the :func:`get_frame_info`
        function.

.. attribute:: as_digested_dict

    Load as a digested dictionary.

.. attribute:: as_undigested_dict

    Load as an undigested dictionary.

Advanced parameter control

.. class:: CompressionParameter()

An :class:~enum.IntEnum containing the advanced compression parameter keys that can be used when compressing data.

The :meth:~.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 :attr:~.compression_level::

  lower, upper = CompressionParameter.compression_level.bounds()

Example setting the :attr:~.window_log to the maximum size::

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

.. method:: 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
  :attr:`~.compression_level`, one may check the result of
  ``CompressionParameter.compression_level.bounds()``.

  Both the lower and upper bounds are inclusive.

.. attribute:: 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 :attr:`COMPRESSION_LEVEL_DEFAULT`.

.. attribute:: 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.

.. attribute:: 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 <= :attr:`~Strategy.dfast`, and improve compression
  speed of strategies > :attr:`~Strategy.dfast`.

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

.. attribute:: 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
  :attr:`~Strategy.fast` strategy. It's still useful when using
  :attr:`~Strategy.dfast` strategy, in which case it defines a secondary
  probe table.

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

.. attribute:: search_log

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

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

.. attribute:: 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 < :attr:`~Strategy.btopt`,
  the effective minimum is ``4``; for all strategies
  > :attr:`~Strategy.fast`, the effective maximum is ``6``.

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

.. attribute:: target_length

  The impact of this field depends on the selected :class:`Strategy`.

  For strategies :attr:`~Strategy.btopt`, :attr:`~Strategy.btultra` and
  :attr:`~Strategy.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 :attr:`~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.

.. attribute:: 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.

  .. seealso:: :class:`Strategy`

.. attribute:: 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
  :attr:`~CompressionParameter.window_log` to 128 MiB except when expressly
  set to a different value. This setting is enabled by default if
  :attr:`!window_log` >= 128 MiB and the compression
  strategy >= :attr:`~Strategy.btopt` (compression level 16+).

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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 :func:`compress` for one-shot compression
  * Providing all of the data to be compressed in the frame in a single
    :meth:`ZstdCompressor.compress` call, with the
    :attr:`ZstdCompressor.FLUSH_FRAME` mode.
  * Calling :meth:`ZstdCompressor.set_pledged_input_size` with the exact
    amount of data that will be provided to the compressor prior to any
    calls to :meth:`ZstdCompressor.compress` for the current frame.
    :meth:`!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.

.. attribute:: 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 :class:`ZstdError` exception is
  raised.

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

.. attribute:: dict_id_flag

  When compressing with a :class:`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.

.. attribute:: nb_workers

  Select how many threads will be spawned to compress in parallel. When
  :attr:`!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.

.. attribute:: job_size

  Size of a compression job, in bytes. This value is enforced only when
  :attr:`~CompressionParameter.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.

.. attribute:: 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 :attr:`~CompressionParameter.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:: DecompressionParameter()

An :class:~enum.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 :meth:~.bounds method can be used on any attribute to get the valid values for that parameter.

Example setting the :attr:~.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)

.. method:: 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.

.. attribute:: 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:: Strategy()

An :class:~enum.IntEnum containing strategies for compression. Higher-numbered strategies correspond to more complex and slower compression.

.. note::

  The values of attributes of :class:`!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:

.. attribute:: fast

.. attribute:: dfast

.. attribute:: greedy

.. attribute:: lazy

.. attribute:: lazy2

.. attribute:: btlazy2

.. attribute:: btopt

.. attribute:: btultra

.. attribute:: btultra2

Miscellaneous

.. function:: get_frame_info(frame_buffer)

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

.. class:: FrameInfo

Metadata related to a Zstandard frame.

.. attribute:: decompressed_size

  The size of the decompressed contents of the frame.

.. attribute:: 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.

.. attribute:: COMPRESSION_LEVEL_DEFAULT

The default compression level for Zstandard: 3.

.. attribute:: zstd_version_info

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

Examples

Reading in a compressed file:

.. code-block:: python

from compression import zstd

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

Creating a compressed file:

.. code-block:: python

from compression import zstd

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

Compressing data in memory:

.. code-block:: python

from compression import zstd

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

Incremental compression:

.. code-block:: python

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:

.. code-block:: python

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:

.. code-block:: python

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?")

:mod:`!compression.zstd` --- Compression compatible with the Zstandard format

:mod:!compression.zstd --- Compression compatible with the Zstandard format

Exceptions

Reading and writing compressed files

Compressing and decompressing data in memory

Zstandard dictionaries

Advanced parameter control

Miscellaneous

Examples

Concatenate all the partial results:

:mod:`!compression.zstd` --- Compression compatible with the Zstandard format