## [521e89]: Doc / lib / libbz2.tex  Maximize  Restore  History

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  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 \section{\module{bz2} --- Compression compatible with \program{bzip2}} \declaremodule{builtin}{bz2} \modulesynopsis{Interface to compression and decompression routines compatible with \program{bzip2}.} \moduleauthor{Gustavo Niemeyer}{niemeyer@conectiva.com} \sectionauthor{Gustavo Niemeyer}{niemeyer@conectiva.com} \versionadded{2.3} This module provides a comprehensive interface for the bz2 compression library. It implements a complete file interface, one-shot (de)compression functions, and types for sequential (de)compression. Here is a resume of the features offered by the bz2 module: \begin{itemize} \item \class{BZ2File} class implements a complete file interface, including \method{readline()}, \method{readlines()}, \method{xreadlines()}, \method{writelines()}, \method{seek()}, etc; \item \class{BZ2File} class implements emulated \method{seek()} support; \item \class{BZ2File} class implements universal newline support; \item \class{BZ2File} class offers an optimized line iteration using the readahead algorithm borrowed from file objects; \item \class{BZ2File} class developed inheriting builtin file type (\code{isinstance(BZ2File(), file) == 1}); \item Sequential (de)compression supported by \class{BZ2Compressor} and \class{BZ2Decompressor} classes; \item One-shot (de)compression supported by \function{compress()} and \function{decompress()} functions; \item Thread safety uses individual locking mechanism; \item Complete inline documentation; \end{itemize} \subsection{(De)compression of files} Handling of compressed files is offered by the \class{BZ2File} class. \begin{classdesc}{BZ2File}{filename \optional{, mode='r'\optional{, buffering=0\optional{, compresslevel=9}}}} Open a bz2 file. Mode can be either \code{'r'} or \code{'w'}, for reading (default) or writing. When opened for writing, the file will be created if it doesn't exist, and truncated otherwise. If the buffering argument is given, \code{0} means unbuffered, and larger numbers specify the buffer size. If compresslevel is given, must be a number between \code{1} and \code{9}. Add a \code{'U'} to mode to open the file for input with universal newline support. Any line ending in the input file will be seen as a \code{'\textbackslash n'} in Python. Also, a file so opened gains the attribute \member{newlines}; the value for this attribute is one of \code{None} (no newline read yet), \code{'\textbackslash r'}, \code{'\textbackslash n'}, \code{'\textbackslash r\textbackslash n'} or a tuple containing all the newline types seen. Universal newlines are available only when reading. \end{classdesc} \begin{methoddesc}[BZ2File]{close}{} Close the file. Sets data attribute \member{closed} to true. A closed file cannot be used for further I/O operations. \method{close()} may be called more than once without error. \end{methoddesc} \begin{methoddesc}[BZ2File]{read}{\optional{size}} Read at most \var{size} uncompressed bytes, returned as a string. If the \var{size} argument is negative or omitted, read until EOF is reached. \end{methoddesc} \begin{methoddesc}[BZ2File]{readline}{\optional{size}} Return the next line from the file, as a string, retaining newline. A non-negative \var{size} argument limits the maximum number of bytes to return (an incomplete line may be returned then). Return an empty string at EOF. \end{methoddesc} \begin{methoddesc}[BZ2File]{readlines}{\optional{size}} Return a list of lines read. The optional \var{size} argument, if given, is an approximate bound on the total number of bytes in the lines returned. \end{methoddesc} \begin{methoddesc}[BZ2File]{xreadlines}{} For backward compatibility. \class{BZ2File} objects now include the performance optimizations previously implemented in the \module{xreadlines} module. \end{methoddesc} \begin{methoddesc}[BZ2File]{\_\_iter\_\_}{} Iterate trough the file lines. Iteration optimization is implemented using the same readahead algorithm available in \class{file} objects. \end{methoddesc} \begin{methoddesc}[BZ2File]{seek}{offset \optional{, whence}} Move to new file position. Argument \var{offset} is a byte count. Optional argument \var{whence} defaults to \code{0} (offset from start of file, offset should be \code{>= 0}); other values are \code{1} (move relative to current position, positive or negative), and \code{2} (move relative to end of file, usually negative, although many platforms allow seeking beyond the end of a file). Note that seeking of bz2 files is emulated, and depending on the parameters the operation may be extremely slow. \end{methoddesc} \begin{methoddesc}[BZ2File]{tell}{} Return the current file position, an integer (may be a long integer). \end{methoddesc} \begin{methoddesc}[BZ2File]{write}{data} Write string \var{data} to file. Note that due to buffering, \method{close()} may be needed before the file on disk reflects the data written. \end{methoddesc} \begin{methoddesc}[BZ2File]{writelines}{sequence_of_strings} Write the sequence of strings to the file. Note that newlines are not added. The sequence can be any iterable object producing strings. This is equivalent to calling write() for each string. \end{methoddesc} \subsection{Sequential (de)compression} Sequential compression and decompression is done using the classes \class{BZ2Compressor} and \class{BZ2Decompressor}. \begin{classdesc}{BZ2Compressor}{\optional{compresslevel=9}} Create a new compressor object. This object may be used to compress data sequentially. If you want to compress data in one shot, use the \function{compress()} function instead. The \var{compresslevel} parameter, if given, must be a number between \code{1} and \code{9}. \end{classdesc} \begin{methoddesc}[BZ2Compressor]{compress}{data} Provide more data to the compressor object. It will return chunks of compressed data whenever possible. When you've finished providing data to compress, call the \method{flush()} method to finish the compression process, and return what is left in internal buffers. \end{methoddesc} \begin{methoddesc}[BZ2Compressor]{flush}{} Finish the compression process and return what is left in internal buffers. You must not use the compressor object after calling this method. \end{methoddesc} \begin{classdesc}{BZ2Decompressor}{} Create a new decompressor object. This object may be used to decompress data sequentially. If you want to decompress data in one shot, use the \function{decompress()} function instead. \end{classdesc} \begin{methoddesc}[BZ2Decompressor]{decompress}{data} Provide more data to the decompressor object. It will return chunks of decompressed data whenever possible. If you try to decompress data after the end of stream is found, \exception{EOFError} will be raised. If any data was found after the end of stream, it'll be ignored and saved in \member{unused\_data} attribute. \end{methoddesc} \subsection{One-shot (de)compression} One-shot compression and decompression is provided trough the \function{compress()} and \function{decompress()} functions. \begin{funcdesc}{compress}{data\optional{, compresslevel=9}} Compress \var{data} in one shot. If you want to compress data sequentially, use an instance of \class{BZ2Compressor} instead. The \var{compresslevel} parameter, if given, must be a number between \code{1} and \code{9}. \end{funcdesc} \begin{funcdesc}{decompress}{} Decompress \var{data} in one shot. If you want to decompress data sequentially, use an instance of \class{BZ2Decompressor} instead. \end{funcdesc}