==================================== gzip -- Read and write GNU zip files ==================================== .. module:: gzip :synopsis: Read and write gzip files :Purpose: Read and write gzip files. :Available In: 1.5.2 and later The gzip module provides a file-like interface to GNU zip files, using :mod:`zlib` to compress and uncompress the data. Writing Compressed Files ======================== The module-level function ``open()`` creates an instance of the file-like class GzipFile. The usual methods for writing and reading data are provided. To write data into a compressed file, open the file with mode ``'w'``. .. include:: gzip_write.py :literal: :start-after: #end_pymotw_header .. {{{cog .. cog.out(run_script(cog.inFile, 'gzip_write.py')) .. }}} :: $ python gzip_write.py application/x-gzip; charset=binary example.txt.gz contains 68 bytes of compressed data .. {{{end}}} Different amounts of compression can be used by passing a *compresslevel* argument. Valid values range from 1 to 9, inclusive. Lower values are faster and result in less compression. Higher values are slower and compress more, up to a point. .. include:: gzip_compresslevel.py :literal: :start-after: #end_pymotw_header The center column of numbers in the output of the script is the size in bytes of the files produced. As you see, for this input data, the higher compression values do not necessarily pay off in decreased storage space. Results will vary, depending on the input data. .. {{{cog .. cog.out(run_script(cog.inFile, 'gzip_compresslevel.py')) .. }}} :: $ python gzip_compresslevel.py Level Size Checksum ----- ---------- --------------------------------- data 754688 e4c0f9433723971563f08a458715119c 1 9839 1ff2fc4d9e466f01aa78856bf50fdad5 2 8260 342d621c603a409214172edd0e8e6838 3 8221 75a64632782808feb2b7519034d3e6c1 4 4160 c445f8379b44186bba1c2cf38ca4109a 5 4160 cdc096dc168637a7bae6174147294d6f 6 4160 841ef69720326a32fd8e28281cdd8f7e 7 4160 a05f486792e120aaf1621aef527fa8ad 8 4160 c03900a4c0d24198d1582e0239784873 9 4160 a6fb55fe8cbaaa10ee7427788839f89b .. {{{end}}} A GzipFile instance also includes a ``writelines()`` method that can be used to write a sequence of strings. .. include:: gzip_writelines.py :literal: :start-after: #end_pymotw_header .. {{{cog .. cog.out(run_script(cog.inFile, 'gzip_writelines.py')) .. }}} :: $ python gzip_writelines.py The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. .. {{{end}}} Reading Compressed Data ======================= To read data back from previously compressed files, simply open the file with mode ``'r'``. .. include:: gzip_read.py :literal: :start-after: #end_pymotw_header This example reads the file written by ``gzip_write.py`` from the previous section. .. {{{cog .. cog.out(run_script(cog.inFile, 'gzip_read.py')) .. }}} :: $ python gzip_read.py Contents of the example file go here. .. {{{end}}} While reading a file, it is also possible to seek and read only part of the data. .. include:: gzip_seek.py :literal: :start-after: #end_pymotw_header The ``seek()`` position is relative to the *uncompressed* data, so the caller does not even need to know that the data file is compressed. .. {{{cog .. cog.out(run_script(cog.inFile, 'gzip_seek.py')) .. }}} :: $ python gzip_seek.py Entire file: Contents of the example file go here. Starting at position 5 for 10 bytes: nts of the True .. {{{end}}} Working with Streams ==================== When working with a data stream instead of a file, use the GzipFile class directly to compress or uncompress it. This is useful when the data is being transmitted over a socket or from read an existing (already open) file handle. A StringIO buffer can also be used. .. include:: gzip_StringIO.py :literal: :start-after: #end_pymotw_header .. note:: When re-reading the previously compressed data, I pass an explicit length to ``read()``. Leaving the length off resulted in a CRC error, possibly because StringIO returned an empty string before reporting EOF. If you are working with streams of compressed data, you may want to prefix the data with an integer representing the actual amount of data to be read. .. {{{cog .. cog.out(run_script(cog.inFile, 'gzip_StringIO.py')) .. }}} :: $ python gzip_StringIO.py UNCOMPRESSED: 300 The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. COMPRESSED: 51 1f8b08001d06215102ff0bc94855284ecc4d55c8c9cc4bd551c82f4b2d5248cc4b0133f4b8424665916401d3e717802c010000 RE-READ: 300 The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. The same line, over and over. .. {{{end}}} .. seealso:: `gzip `_ The standard library documentation for this module. :mod:`zlib` The zlib module is a lower-level interface to gzip compression. :mod:`zipfile` The zipfile module gives access to ZIP archives. :mod:`bz2` The bz2 module uses the bzip2 compression format. :mod:`tarfile` The tarfile module includes built-in support for reading compressed tar archives.