Doc/lib/libbinascii.tex

   1 \section{\module{binascii} ---
   2          Convert between binary and \ASCII}
   3
   4 \declaremodule{builtin}{binascii}
   5 \modulesynopsis{Tools for converting between binary and various
   6                 \ASCII-encoded binary representations.}
   7
   8
   9 The \module{binascii} module contains a number of methods to convert
  10 between binary and various \ASCII-encoded binary
  11 representations. Normally, you will not use these functions directly
  12 but use wrapper modules like \refmodule{uu}\refstmodindex{uu} or
  13 \refmodule{binhex}\refstmodindex{binhex} instead, this module solely
  14 exists because bit-manipulation of large amounts of data is slow in
  15 Python.
  16
  17 The \module{binascii} module defines the following functions:
  18
  19 \begin{funcdesc}{a2b_uu}{string}
  20 Convert a single line of uuencoded data back to binary and return the
  21 binary data. Lines normally contain 45 (binary) bytes, except for the
  22 last line. Line data may be followed by whitespace.
  23 \end{funcdesc}
  24
  25 \begin{funcdesc}{b2a_uu}{data}
  26 Convert binary data to a line of \ASCII{} characters, the return value
  27 is the converted line, including a newline char. The length of
  28 \var{data} should be at most 45.
  29 \end{funcdesc}
  30
  31 \begin{funcdesc}{a2b_base64}{string}
  32 Convert a block of base64 data back to binary and return the
  33 binary data. More than one line may be passed at a time.
  34 \end{funcdesc}
  35
  36 \begin{funcdesc}{b2a_base64}{data}
  37 Convert binary data to a line of \ASCII{} characters in base64 coding.
  38 The return value is the converted line, including a newline char.
  39 The length of \var{data} should be at most 57 to adhere to the base64
  40 standard.
  41 \end{funcdesc}
  42
  43 \begin{funcdesc}{a2b_qp}{string\optional{, header}}
  44 Convert a block of quoted-printable data back to binary and return the
  45 binary data. More than one line may be passed at a time.
  46 If the optional argument \var{header} is present and true, underscores
  47 will be decoded as spaces.
  48 \end{funcdesc}
  49
  50 \begin{funcdesc}{b2a_qp}{data\optional{, quotetabs, istext, header}}
  51 Convert binary data to a line(s) of \ASCII{} characters in
  52 quoted-printable encoding.  The return value is the converted line(s).
  53 If the optional argument \var{quotetabs} is present and true, all tabs
  54 and spaces will be encoded.  If the optional argument \var{header} is
  55 present and true, spaces will be encoded as underscores per RFC1522.
  56 If the optional argument \var{header} is present and false, newline
  57 characters will be encoded as well, otherwise linefeed conversion might
  58 corrupt the binary data stream.
  59 \end{funcdesc}
  60
  61 \begin{funcdesc}{a2b_hqx}{string}
  62 Convert binhex4 formatted \ASCII{} data to binary, without doing
  63 RLE-decompression. The string should contain a complete number of
  64 binary bytes, or (in case of the last portion of the binhex4 data)
  65 have the remaining bits zero.
  66 \end{funcdesc}
  67
  68 \begin{funcdesc}{rledecode_hqx}{data}
  69 Perform RLE-decompression on the data, as per the binhex4
  70 standard. The algorithm uses \code{0x90} after a byte as a repeat
  71 indicator, followed by a count. A count of \code{0} specifies a byte
  72 value of \code{0x90}. The routine returns the decompressed data,
  73 unless data input data ends in an orphaned repeat indicator, in which
  74 case the \exception{Incomplete} exception is raised.
  75 \end{funcdesc}
  76
  77 \begin{funcdesc}{rlecode_hqx}{data}
  78 Perform binhex4 style RLE-compression on \var{data} and return the
  79 result.
  80 \end{funcdesc}
  81
  82 \begin{funcdesc}{b2a_hqx}{data}
  83 Perform hexbin4 binary-to-\ASCII{} translation and return the
  84 resulting string. The argument should already be RLE-coded, and have a
  85 length divisible by 3 (except possibly the last fragment).
  86 \end{funcdesc}
  87
  88 \begin{funcdesc}{crc_hqx}{data, crc}
  89 Compute the binhex4 crc value of \var{data}, starting with an initial
  90 \var{crc} and returning the result.
  91 \end{funcdesc}
  92
  93 \begin{funcdesc}{crc32}{data\optional{, crc}}
  94 Compute CRC-32, the 32-bit checksum of data, starting with an initial
  95 crc.  This is consistent with the ZIP file checksum.  Since the
  96 algorithm is designed for use as a checksum algorithm, it is not
  97 suitable for use as a general hash algorithm.  Use as follows:
  98 \begin{verbatim}
  99     print binascii.crc32("hello world")
 100     # Or, in two pieces:
 101     crc = binascii.crc32("hello")
 102     crc = binascii.crc32(" world", crc)
 103     print crc
 104 \end{verbatim}
 105 \end{funcdesc}
 106
 107 \begin{funcdesc}{b2a_hex}{data}
 108 \funcline{hexlify}{data}
 109 Return the hexadecimal representation of the binary \var{data}.  Every
 110 byte of \var{data} is converted into the corresponding 2-digit hex
 111 representation.  The resulting string is therefore twice as long as
 112 the length of \var{data}.
 113 \end{funcdesc}
 114
 115 \begin{funcdesc}{a2b_hex}{hexstr}
 116 \funcline{unhexlify}{hexstr}
 117 Return the binary data represented by the hexadecimal string
 118 \var{hexstr}.  This function is the inverse of \function{b2a_hex()}.
 119 \var{hexstr} must contain an even number of hexadecimal digits (which
 120 can be upper or lower case), otherwise a \exception{TypeError} is
 121 raised.
 122 \end{funcdesc}
 123
 124 \begin{excdesc}{Error}
 125 Exception raised on errors. These are usually programming errors.
 126 \end{excdesc}
 127
 128 \begin{excdesc}{Incomplete}
 129 Exception raised on incomplete data. These are usually not programming
 130 errors, but may be handled by reading a little more data and trying
 131 again.
 132 \end{excdesc}
 133
 134
 135 \begin{seealso}
 136   \seemodule{base64}{Support for base64 encoding used in MIME email messages.}
 137
 138   \seemodule{binhex}{Support for the binhex format used on the Macintosh.}
 139
 140   \seemodule{uu}{Support for UU encoding used on \UNIX.}
 141
 142   \seemodule{quopri}{Support for quoted-printable encoding used in MIME email messages. }
 143 \end{seealso}