# 12.13 `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` or `binhex` instead, this module solely exists because bit-manipulation of large amounts of data is slow in Python.

The `binascii` module defines the following functions:

`a2b_uu`(string)
  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.

`b2a_uu`(data)
  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 45.

`a2b_base64`(string)
  Convert a block of base64 data back to binary and return the binary data. More than one line may be passed at a time.

`b2a_base64`(data)
  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.

`a2b_qp`(string[, header])
  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.

`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 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 stream.

`a2b_hqx`(string)
  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.

`rledecode_hqx`(data)
  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.

`rlecode_hqx`(data)
  Perform binhex4 style RLE-compression on data and return the result.

`b2a_hqx`(data)
  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).

`crc_hqx`(data, crc)
  Compute the binhex4 crc value of data, starting with an initial crc and returning the result.

`crc32`(data[, crc])
  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)
            print crc

`b2a_hex`(data)
`hexlify`(data)
  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.

`a2b_hex`(hexstr)
`unhexlify`(hexstr)
  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 `Error`
  Exception raised on errors. These are usually programming errors.

exception `Incomplete`
  Exception raised on incomplete data. These are usually not programming errors, but may be handled by reading a little more data and trying again.

See Also:

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. .