18.14. binascii — Convert between binary and ASCII
The binascii module contains a number of methods to convert between
binary and various ASCII-encoded binary representations. Normally, you will not
use these functions directly but use wrapper modules like uu,
base64, or binhex instead. The binascii module contains
low-level functions written in C for greater speed that are used by the
The binascii module defines the following functions:
- Convert a single line of uuencoded data back to binary and return the binary
data. Lines normally contain 45 (binary) bytes, except for the last line. Line
data may be followed by whitespace.
- Convert binary data to a line of ASCII characters, the return value is the
converted line, including a newline char. The length of data should be at most
- Convert a block of base64 data back to binary and return the binary data. More
than one line may be passed at a time.
- Convert binary data to a line of ASCII characters in base64 coding. The return
value is the converted line, including a newline char. The length of data
should be at most 57 to adhere to the base64 standard.
- Convert a block of quoted-printable data back to binary and return the binary
data. More than one line may be passed at a time. If the optional argument
header is present and true, underscores will be decoded as spaces.
binascii.b2a_qp(data[, quotetabs, istext, header])
- Convert binary data to a line(s) of ASCII characters in quoted-printable
encoding. The return value is the converted line(s). If the optional argument
quotetabs is present and true, all tabs and spaces will be encoded. If the
optional argument istext is present and true, newlines are not encoded but
trailing whitespace will be encoded. If the optional argument header is
present and true, spaces will be encoded as underscores per RFC1522. If the
optional argument header is present and false, newline characters will be
encoded as well; otherwise linefeed conversion might corrupt the binary data
- Convert binhex4 formatted ASCII data to binary, without doing RLE-decompression.
The string should contain a complete number of binary bytes, or (in case of the
last portion of the binhex4 data) have the remaining bits zero.
- Perform RLE-decompression on the data, as per the binhex4 standard. The
algorithm uses 0x90 after a byte as a repeat indicator, followed by a count.
A count of 0 specifies a byte value of 0x90. The routine returns the
decompressed data, unless data input data ends in an orphaned repeat indicator,
in which case the Incomplete exception is raised.
- Perform binhex4 style RLE-compression on data and return the result.
- Perform hexbin4 binary-to-ASCII translation and return the resulting string. The
argument should already be RLE-coded, and have a length divisible by 3 (except
possibly the last fragment).
- Compute the binhex4 crc value of data, starting with an initial crc and
returning the result.
Compute CRC-32, the 32-bit checksum of data, starting with an initial crc. This
is consistent with the ZIP file checksum. Since the algorithm is designed for
use as a checksum algorithm, it is not suitable for use as a general hash
algorithm. Use as follows:
print binascii.crc32("hello world")
# Or, in two pieces:
crc = binascii.crc32("hello")
crc = binascii.crc32(" world", crc) & 0xffffffff
print 'crc32 = 0x%08x' % crc
To generate the same numeric value across all Python versions and
platforms use crc32(data) & 0xffffffff. If you are only using
the checksum in packed binary format this is not necessary as the
return value is the correct 32bit binary representation
regardless of sign.
Changed in version 2.6: The return value is in the range [-2**31, 2**31-1]
regardless of platform. In the past the value would be signed on
some platforms and unsigned on others. Use & 0xffffffff on the
value if you want it to match 3.0 behavior.
Changed in version 3.0: The return value is unsigned and in the range [0, 2**32-1]
regardless of platform.
- Return the hexadecimal representation of the binary data. Every byte of
data is converted into the corresponding 2-digit hex representation. The
resulting string is therefore twice as long as the length of data.
- Return the binary data represented by the hexadecimal string hexstr. This
function is the inverse of b2a_hex(). hexstr must contain an even number
of hexadecimal digits (which can be upper or lower case), otherwise a
TypeError is raised.
- Exception raised on errors. These are usually programming errors.
- Exception raised on incomplete data. These are usually not programming errors,
but may be handled by reading a little more data and trying again.
- Module base64
- Support for base64 encoding used in MIME email messages.
- Module binhex
- Support for the binhex format used on the Macintosh.
- Module uu
- Support for UU encoding used on Unix.
- Module quopri
- Support for quoted-printable encoding used in MIME email messages.