2 :mod:`binascii` --- Convert between binary and ASCII
3 ====================================================
6 :synopsis: Tools for converting between binary and various ASCII-encoded binary
15 The :mod:`binascii` module contains a number of methods to convert between
16 binary and various ASCII-encoded binary representations. Normally, you will not
17 use these functions directly but use wrapper modules like :mod:`uu`,
18 :mod:`base64`, or :mod:`binhex` instead. The :mod:`binascii` module contains
19 low-level functions written in C for greater speed that are used by the
22 The :mod:`binascii` module defines the following functions:
25 .. function:: a2b_uu(string)
27 Convert a single line of uuencoded data back to binary and return the binary
28 data. Lines normally contain 45 (binary) bytes, except for the last line. Line
29 data may be followed by whitespace.
32 .. function:: b2a_uu(data)
34 Convert binary data to a line of ASCII characters, the return value is the
35 converted line, including a newline char. The length of *data* should be at most
39 .. function:: a2b_base64(string)
41 Convert a block of base64 data back to binary and return the binary data. More
42 than one line may be passed at a time.
45 .. function:: b2a_base64(data)
47 Convert binary data to a line of ASCII characters in base64 coding. The return
48 value is the converted line, including a newline char. The length of *data*
49 should be at most 57 to adhere to the base64 standard.
52 .. function:: a2b_qp(string[, header])
54 Convert a block of quoted-printable data back to binary and return the binary
55 data. More than one line may be passed at a time. If the optional argument
56 *header* is present and true, underscores will be decoded as spaces.
59 .. function:: b2a_qp(data[, quotetabs, istext, header])
61 Convert binary data to a line(s) of ASCII characters in quoted-printable
62 encoding. The return value is the converted line(s). If the optional argument
63 *quotetabs* is present and true, all tabs and spaces will be encoded. If the
64 optional argument *istext* is present and true, newlines are not encoded but
65 trailing whitespace will be encoded. If the optional argument *header* is
66 present and true, spaces will be encoded as underscores per RFC1522. If the
67 optional argument *header* is present and false, newline characters will be
68 encoded as well; otherwise linefeed conversion might corrupt the binary data
72 .. function:: a2b_hqx(string)
74 Convert binhex4 formatted ASCII data to binary, without doing RLE-decompression.
75 The string should contain a complete number of binary bytes, or (in case of the
76 last portion of the binhex4 data) have the remaining bits zero.
79 .. function:: rledecode_hqx(data)
81 Perform RLE-decompression on the data, as per the binhex4 standard. The
82 algorithm uses ``0x90`` after a byte as a repeat indicator, followed by a count.
83 A count of ``0`` specifies a byte value of ``0x90``. The routine returns the
84 decompressed data, unless data input data ends in an orphaned repeat indicator,
85 in which case the :exc:`Incomplete` exception is raised.
88 .. function:: rlecode_hqx(data)
90 Perform binhex4 style RLE-compression on *data* and return the result.
93 .. function:: b2a_hqx(data)
95 Perform hexbin4 binary-to-ASCII translation and return the resulting string. The
96 argument should already be RLE-coded, and have a length divisible by 3 (except
97 possibly the last fragment).
100 .. function:: crc_hqx(data, crc)
102 Compute the binhex4 crc value of *data*, starting with an initial *crc* and
103 returning the result.
106 .. function:: crc32(data[, crc])
108 Compute CRC-32, the 32-bit checksum of data, starting with an initial crc. This
109 is consistent with the ZIP file checksum. Since the algorithm is designed for
110 use as a checksum algorithm, it is not suitable for use as a general hash
111 algorithm. Use as follows::
113 print binascii.crc32("hello world")
115 crc = binascii.crc32("hello")
116 crc = binascii.crc32(" world", crc) & 0xffffffff
117 print 'crc32 = 0x%08x' % crc
120 To generate the same numeric value across all Python versions and
121 platforms use crc32(data) & 0xffffffff. If you are only using
122 the checksum in packed binary format this is not necessary as the
123 return value is the correct 32bit binary representation
126 .. versionchanged:: 2.6
127 The return value is in the range [-2**31, 2**31-1]
128 regardless of platform. In the past the value would be signed on
129 some platforms and unsigned on others. Use & 0xffffffff on the
130 value if you want it to match 3.0 behavior.
132 .. versionchanged:: 3.0
133 The return value is unsigned and in the range [0, 2**32-1]
134 regardless of platform.
137 .. function:: b2a_hex(data)
140 Return the hexadecimal representation of the binary *data*. Every byte of
141 *data* is converted into the corresponding 2-digit hex representation. The
142 resulting string is therefore twice as long as the length of *data*.
145 .. function:: a2b_hex(hexstr)
148 Return the binary data represented by the hexadecimal string *hexstr*. This
149 function is the inverse of :func:`b2a_hex`. *hexstr* must contain an even number
150 of hexadecimal digits (which can be upper or lower case), otherwise a
151 :exc:`TypeError` is raised.
156 Exception raised on errors. These are usually programming errors.
159 .. exception:: Incomplete
161 Exception raised on incomplete data. These are usually not programming errors,
162 but may be handled by reading a little more data and trying again.
168 Support for base64 encoding used in MIME email messages.
171 Support for the binhex format used on the Macintosh.
174 Support for UU encoding used on Unix.
177 Support for quoted-printable encoding used in MIME email messages.