1 :mod:`binascii` --- Convert between binary and ASCII 2 ==================================================== 3 4 .. module:: binascii 5 :synopsis: Tools for converting between binary and various ASCII-encoded binary 6 representations. 7 8 .. index:: 9 module: uu 10 module: base64 11 module: binhex 12 13 -------------- 14 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 20 higher-level modules. 21 22 .. note:: 23 24 ``a2b_*`` functions accept Unicode strings containing only ASCII characters. 25 Other functions only accept :term:`bytes-like objects <bytes-like object>` (such as 26 :class:`bytes`, :class:`bytearray` and other objects that support the buffer 27 protocol). 28 29 .. versionchanged:: 3.3 30 ASCII-only unicode strings are now accepted by the ``a2b_*`` functions. 31 32 33 The :mod:`binascii` module defines the following functions: 34 35 36 .. function:: a2b_uu(string) 37 38 Convert a single line of uuencoded data back to binary and return the binary 39 data. Lines normally contain 45 (binary) bytes, except for the last line. Line 40 data may be followed by whitespace. 41 42 43 .. function:: b2a_uu(data, *, backtick=False) 44 45 Convert binary data to a line of ASCII characters, the return value is the 46 converted line, including a newline char. The length of *data* should be at most 47 45. If *backtick* is true, zeros are represented by ``'`'`` instead of spaces. 48 49 .. versionchanged:: 3.7 50 Added the *backtick* parameter. 51 52 53 .. function:: a2b_base64(string) 54 55 Convert a block of base64 data back to binary and return the binary data. More 56 than one line may be passed at a time. 57 58 59 .. function:: b2a_base64(data, *, newline=True) 60 61 Convert binary data to a line of ASCII characters in base64 coding. The return 62 value is the converted line, including a newline char if *newline* is 63 true. The output of this function conforms to :rfc:`3548`. 64 65 .. versionchanged:: 3.6 66 Added the *newline* parameter. 67 68 69 .. function:: a2b_qp(data, header=False) 70 71 Convert a block of quoted-printable data back to binary and return the binary 72 data. More than one line may be passed at a time. If the optional argument 73 *header* is present and true, underscores will be decoded as spaces. 74 75 76 .. function:: b2a_qp(data, quotetabs=False, istext=True, header=False) 77 78 Convert binary data to a line(s) of ASCII characters in quoted-printable 79 encoding. The return value is the converted line(s). If the optional argument 80 *quotetabs* is present and true, all tabs and spaces will be encoded. If the 81 optional argument *istext* is present and true, newlines are not encoded but 82 trailing whitespace will be encoded. If the optional argument *header* is 83 present and true, spaces will be encoded as underscores per :rfc:`1522`. If the 84 optional argument *header* is present and false, newline characters will be 85 encoded as well; otherwise linefeed conversion might corrupt the binary data 86 stream. 87 88 89 .. function:: a2b_hqx(string) 90 91 Convert binhex4 formatted ASCII data to binary, without doing RLE-decompression. 92 The string should contain a complete number of binary bytes, or (in case of the 93 last portion of the binhex4 data) have the remaining bits zero. 94 95 96 .. function:: rledecode_hqx(data) 97 98 Perform RLE-decompression on the data, as per the binhex4 standard. The 99 algorithm uses ``0x90`` after a byte as a repeat indicator, followed by a count. 100 A count of ``0`` specifies a byte value of ``0x90``. The routine returns the 101 decompressed data, unless data input data ends in an orphaned repeat indicator, 102 in which case the :exc:`Incomplete` exception is raised. 103 104 .. versionchanged:: 3.2 105 Accept only bytestring or bytearray objects as input. 106 107 108 .. function:: rlecode_hqx(data) 109 110 Perform binhex4 style RLE-compression on *data* and return the result. 111 112 113 .. function:: b2a_hqx(data) 114 115 Perform hexbin4 binary-to-ASCII translation and return the resulting string. The 116 argument should already be RLE-coded, and have a length divisible by 3 (except 117 possibly the last fragment). 118 119 120 .. function:: crc_hqx(data, value) 121 122 Compute a 16-bit CRC value of *data*, starting with *value* as the 123 initial CRC, and return the result. This uses the CRC-CCITT polynomial 124 *x*:sup:`16` + *x*:sup:`12` + *x*:sup:`5` + 1, often represented as 125 0x1021. This CRC is used in the binhex4 format. 126 127 128 .. function:: crc32(data[, value]) 129 130 Compute CRC-32, the 32-bit checksum of *data*, starting with an 131 initial CRC of *value*. The default initial CRC is zero. The algorithm 132 is consistent with the ZIP file checksum. Since the algorithm is designed for 133 use as a checksum algorithm, it is not suitable for use as a general hash 134 algorithm. Use as follows:: 135 136 print(binascii.crc32(b"hello world")) 137 # Or, in two pieces: 138 crc = binascii.crc32(b"hello") 139 crc = binascii.crc32(b" world", crc) 140 print('crc32 = {:#010x}'.format(crc)) 141 142 .. versionchanged:: 3.0 143 The result is always unsigned. 144 To generate the same numeric value across all Python versions and 145 platforms, use ``crc32(data) & 0xffffffff``. 146 147 148 .. function:: b2a_hex(data) 149 hexlify(data) 150 151 Return the hexadecimal representation of the binary *data*. Every byte of 152 *data* is converted into the corresponding 2-digit hex representation. The 153 returned bytes object is therefore twice as long as the length of *data*. 154 155 Similar functionality (but returning a text string) is also conveniently 156 accessible using the :meth:`bytes.hex` method. 157 158 .. function:: a2b_hex(hexstr) 159 unhexlify(hexstr) 160 161 Return the binary data represented by the hexadecimal string *hexstr*. This 162 function is the inverse of :func:`b2a_hex`. *hexstr* must contain an even number 163 of hexadecimal digits (which can be upper or lower case), otherwise an 164 :exc:`Error` exception is raised. 165 166 Similar functionality (accepting only text string arguments, but more 167 liberal towards whitespace) is also accessible using the 168 :meth:`bytes.fromhex` class method. 169 170 .. exception:: Error 171 172 Exception raised on errors. These are usually programming errors. 173 174 175 .. exception:: Incomplete 176 177 Exception raised on incomplete data. These are usually not programming errors, 178 but may be handled by reading a little more data and trying again. 179 180 181 .. seealso:: 182 183 Module :mod:`base64` 184 Support for RFC compliant base64-style encoding in base 16, 32, 64, 185 and 85. 186 187 Module :mod:`binhex` 188 Support for the binhex format used on the Macintosh. 189 190 Module :mod:`uu` 191 Support for UU encoding used on Unix. 192 193 Module :mod:`quopri` 194 Support for quoted-printable encoding used in MIME email messages. 195
