mirror of https://github.com/python/cpython.git
100 lines
4.1 KiB
TeX
100 lines
4.1 KiB
TeX
\section{Built-in Module \sectcode{zlib}}
|
|
\bimodindex{zlib}
|
|
|
|
For applications that require data compression, the functions in this
|
|
module allow compression and decompression, using the zlib library,
|
|
which is based on GNU zip. The zlib library has its own home page at
|
|
\code{http://www.cdrom.com/pub/infozip/zlib/}.
|
|
Version 1.0.4 is the most recent version as of April 30, 1997; use a
|
|
later version if one is available.
|
|
|
|
The available functions in this module are:
|
|
|
|
\renewcommand{\indexsubitem}{(in module zlib)}
|
|
\begin{funcdesc}{adler32}{string\optional{\, value}}
|
|
Computes a Adler-32 checksum of \var{string}. (An Adler-32
|
|
checksum is almost as reliable as a CRC32 but can be computed much
|
|
more quickly.) If \var{value} is present, it is used as the
|
|
starting value of the checksum; otherwise, a fixed default value is
|
|
used. This allows computing a running checksum over the
|
|
concatenation of several input strings. The algorithm is not
|
|
cryptographically strong, and should not be used for
|
|
authentication or digital signatures.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{compress}{string\optional{\, level}}
|
|
Compresses the data in \var{string}, returning a string contained
|
|
compressed data. \var{level} is an integer from 1 to 9 controlling
|
|
the level of compression; 1 is fastest and produces the least
|
|
compression, 9 is slowest and produces the most. The default value is
|
|
6. Raises the \code{zlib.error} exception if any error occurs.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{compressobj}{\optional{level}}
|
|
Returns a compression object, to be used for compressing data streams
|
|
that won't fit into memory at once. \var{level} is an integer from
|
|
1 to 9 controlling the level of compression; 1 is fastest and
|
|
produces the least compression, 9 is slowest and produces the most.
|
|
The default value is 6.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{crc32}{string\optional{\, value}}
|
|
Computes a CRC (Cyclic Redundancy Check) sum of \var{string}. If
|
|
\var{value} is present, it is used as the starting value of the
|
|
checksum; otherwise, a fixed default value is used. This allows
|
|
computing a running checksum over the concatenation of several
|
|
input strings. The algorithm is not cryptographically strong, and
|
|
should not be used for authentication or digital signatures.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{decompress}{string}
|
|
Decompresses the data in \var{string}, returning a string containing
|
|
the uncompressed data. Raises the \code{zlib.error} exception if any
|
|
error occurs.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{decompressobj}{\optional{wbits}}
|
|
Returns a compression object, to be used for decompressing data streams
|
|
that won't fit into memory at once. The \var{wbits} parameter
|
|
controls the size of the window buffer; usually this can be left
|
|
alone.
|
|
\end{funcdesc}
|
|
|
|
Compression objects support the following methods:
|
|
|
|
\begin{funcdesc}{compress}{string}
|
|
Compress \var{string}, returning a string containing compressed data
|
|
for at least part of the data in \var{string}. This data should be
|
|
concatenated to the output produced by any preceding calls to the
|
|
\code{compress()} method. Some input may be kept in internal buffers
|
|
for later processing.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{flush}{}
|
|
All pending input is processed, and an string containing the remaining
|
|
compressed output is returned. After calling \code{flush()}, the
|
|
\code{compress()} method cannot be called again; the only realistic
|
|
action is to delete the object.
|
|
\end{funcdesc}
|
|
|
|
Decompression objects support the following methods:
|
|
|
|
\begin{funcdesc}{decompress}{string}
|
|
Decompress \var{string}, returning a string containing the
|
|
uncompressed data corresponding to at least part of the data in
|
|
\var{string}. This data should be concatenated to the output produced
|
|
by any preceding calls to the
|
|
\code{decompress()} method. Some of the input data may be preserved
|
|
in internal buffers for later processing.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{flush}{}
|
|
All pending input is processed, and a string containing the remaining
|
|
uncompressed output is returned. After calling \code{flush()}, the
|
|
\code{decompress()} method cannot be called again; the only realistic
|
|
action is to delete the object.
|
|
\end{funcdesc}
|
|
|
|
|
|
|