kopia lustrzana https://github.com/micropython/micropython
83 wiersze
3.7 KiB
ReStructuredText
83 wiersze
3.7 KiB
ReStructuredText
:mod:`zlib` -- zlib compression & decompression
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===============================================
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.. module:: zlib
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:synopsis: zlib compression & decompression
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|see_cpython_module| :mod:`python:zlib`.
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This module allows compression and decompression of binary data with the
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`DEFLATE algorithm <https://en.wikipedia.org/wiki/DEFLATE>`_
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(commonly used in the zlib library and gzip archiver).
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.. note:: Prefer to use :class:`deflate.DeflateIO` instead of the functions in this
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module as it provides a streaming interface to compression and decompression
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which is convenient and more memory efficient when working with reading or
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writing compressed data to a file, socket, or stream.
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**Availability:**
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* From MicroPython v1.21 onwards, this module may not be present by default on
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all MicroPython firmware as it duplicates functionality available in
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the :mod:`deflate <deflate>` module.
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* A copy of this module can be installed (or frozen)
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from :term:`micropython-lib` (`source <https://github.com/micropython/micropython-lib/blob/master/python-stdlib/zlib/zlib.py>`_).
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See :ref:`packages` for more information. This documentation describes that module.
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* Requires the built-in :mod:`deflate <deflate>` module (available since MicroPython v1.21)
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* Compression support will only be available if compression support is enabled
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in the built-in :mod:`deflate <deflate>` module.
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Functions
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---------
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.. function:: decompress(data, wbits=15, /)
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Decompresses *data* into a bytes object.
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The *wbits* parameter works the same way as for :meth:`zlib.compress`
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with the following additional valid values:
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* ``0``: Automatically determine the window size from the zlib header
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(*data* must be in zlib format).
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* ``35`` to ``47``: Auto-detect either the zlib or gzip format.
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As for :meth:`zlib.compress`, see the :mod:`CPython documentation for zlib <python:zlib>`
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for more information about the *wbits* parameter. As for :meth:`zlib.compress`,
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MicroPython also supports smaller window sizes than CPython. See more
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:ref:`MicroPython-specific details <deflate_wbits>` in the
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:mod:`deflate <deflate>` module documentation.
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If the data to be decompressed requires a larger window size, it will
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fail during decompression.
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.. function:: compress(data, wbits=15, /)
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Compresses *data* into a bytes object.
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*wbits* allows you to configure the DEFLATE dictionary window size and the
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output format. The window size allows you to trade-off memory usage for
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compression level. A larger window size will allow the compressor to
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reference fragments further back in the input. The output formats are "raw"
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DEFLATE (no header/footer), zlib, and gzip, where the latter two
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include a header and checksum.
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The low four bits of the absolute value of *wbits* set the base-2 logarithm of
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the DEFLATE dictionary window size. So for example, ``wbits=10``,
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``wbits=-10``, and ``wbits=26`` all set the window size to 1024 bytes. Valid
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window sizes are ``5`` to ``15`` inclusive (corresponding to 32 to 32k bytes).
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Negative values of *wbits* between ``-5`` and ``-15`` correspond to "raw"
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output mode, positive values between ``5`` and ``15`` correspond to zlib
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output mode, and positive values between ``21`` and ``31`` correspond to
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gzip output mode.
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See the :mod:`CPython documentation for zlib <python:zlib>` for more
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information about the *wbits* parameter. Note that MicroPython allows
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for smaller window sizes, which is useful when memory is constrained while
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still achieving a reasonable level of compression. It also speeds up
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the compressor. See more :ref:`MicroPython-specific details <deflate_wbits>`
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in the :mod:`deflate <deflate>` module documentation.
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