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Rewritten a bit to address some criticism in the newsgroup.

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Guido van Rossum 1998-07-06 20:47:40 +00:00
parent 5f574aace9
commit 7bda89f694
1 changed files with 39 additions and 26 deletions
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Doc/lib/libgzip.tex
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@ -9,39 +9,52 @@ class to read and write \program{gzip}-format files, automatically
compressing or decompressing the data so it looks like an ordinary
file object.
\class{GzipFile} objects simulate most of the methods of a file
object, though it's not possible to use the \method{seek()} and
\method{tell()} methods to access the file randomly.
\withsubitem{(class in gzip)}{\ttindex{GzipFile}}
The module defines the following items:
\begin{classdesc}{GzipFile}{\optional{filename\optional{, mode\optional{,
compresslevel\optional{, fileobj}}}}}
Constructor for the \class{GzipFile} class, which simulates most of
the methods of a file object, with the exception of the
\method{seek()} and \method{tell()} methods. At least one of
\var{fileobj} and \var{filename} must be given a non-trivial value.
\begin{funcdesc}{open}{fileobj\optional{, filename\optional{,
mode\optional{, compresslevel}}}}
Returns a new \class{GzipFile} object on top of \var{fileobj}, which
can be a regular file, a \class{StringIO} object, or any object which
simulates a file.
The new class instance is based on \var{fileobj}, which can be a
regular file, a \class{StringIO} object, or any other object which
simulates a file. It defaults to \code{None}, in which case
\var{filename} is opened to provide a file object.
The \program{gzip} file format includes the original filename of the
uncompressed file; when opening a \class{GzipFile} object for
writing, it can be set by the \var{filename} argument. The default
value is an empty string.
When \var{fileobj} is not \code{None}, the \var{filename} argument is
only used to be included in the \program{gzip} file header, which may
includes the original filename of the uncompressed file. It defaults
to the filename of \var{fileobj}, if discernible; otherwise, it
defaults to the empty string, and in this case the original filename
is not included in the header.
\var{mode} can be either \code{'r'} or \code{'w'} depending on
whether the file will be read or written. \var{compresslevel} is an
integer from \code{1} to \code{9} controlling the level of
compression; \code{1} is fastest and produces the least compression,
and \code{9} is slowest and produces the most compression. The
default value of \var{compresslevel} is \code{9}.
The \var{mode} argument can be either \code{'r'} or \code{'w'},
depending on whether the file will be read or written. The default is
the mode of \var{fileobj} if discernible; otherwise, the default is
\code{'r'}.
Calling a \class{GzipFile} object's \method{close()} method does not
close \var{fileobj}, since you might wish to append more material
after the compressed data. This also allows you to pass a
\class{StringIO} object opened for writing as \var{fileobj}, and
retrieve the resulting memory buffer using the \class{StringIO}
object's \method{getvalue()} method.
The \var{compresslevel} argument is an integer from \code{1} to
\code{9} controlling the level of compression; \code{1} is fastest and
produces the least compression, and \code{9} is slowest and produces
the most compression. The default is \code{9}.
Calling a \class{GzipFile} object's \method{close()} method does not
close \var{fileobj}, since you might wish to append more material
after the compressed data. This also allows you to pass a
\class{StringIO} object opened for writing as \var{fileobj}, and
retrieve the resulting memory buffer using the \class{StringIO}
object's \method{getvalue()} method.
\end{classdesc}
\begin{funcdesc}{open}{filename\optional{, mode\optional{, compresslevel}}}
This is a shorthand for \code{GzipFile(\var{filename},}
\code{\var{mode},} \code{\var{compresslevel})}. The \var{filename}
argument is required; \var{mode} defaults to \code{'r'} and
\var{compresslevel} defaults to \code{9}.
\end{funcdesc}
\begin{seealso}
\seemodule{zlib}{the basic data compression module}
\end{seealso}