Python: convert string to packed hex ( '01020304' -> '\x01\x02\x03\x04' )

Question

I'm trying to convert a string of numbers into a 'packed hex' format.

For example: '01020304' -> '\x01\x02\x03\x04'

I have it working, but I expect there are better (faster, cleaner) more pythonic ways to do this?

def split_len(seq, length):
    return [seq[i:i+length] for i in range(0, len(seq), length)]

def ascii_to_packed_hex(string_data): 
    r"""
    >>> ascii_to_packed_hex('01')
    '\x01'

    >>> ascii_to_packed_hex('0102030405')
    '\x01\x02\x03\x04\x05'

    >>> ascii_to_packed_hex('fafbfcfd')
    '\xfa\xfb\xfc\xfd'

    >>> ascii_to_packed_hex('31323334')
    '1234'
    """               
    hex_data=''
    string_data = string_data.encode('iso-8859-1')
    string_parts = split_len(string_data, 2)

    if len(string_parts)>=1:
        for each_part in string_parts:
            encoded_part = each_part[:2]
            ascii_part   = each_part[2:]
            encoded_part_as_hex = string.atoi(encoded_part,base=16)
            encoded_part_as_hex = chr(encoded_part_as_hex)
            hex_data = hex_data + encoded_part_as_hex + ascii_part
        return hex_data
    else:
        return string_data

    import doctest
    doctest.testmod()

Answer 1

Use binascii, which is in the standard library:

import binascii, doctest

def ascii_to_packed_hex(string_data): 
    r"""
    >>> binascii.a2b_hex('01')
    '\x01'
    >>> binascii.a2b_hex('0102030405')
    '\x01\x02\x03\x04\x05'
    >>> binascii.a2b_hex('fafbfcfd')
    '\xfa\xfb\xfc\xfd'
    >>> binascii.a2b_hex('31323334')
    '1234'
    """
    doctest.testmod()

Answer 2

In Python2 you can use use str.decode()

>>> '01'.decode('hex')
'\x01'
>>> '0102030405'.decode('hex')
'\x01\x02\x03\x04\x05'
>>> 'fafbfcfd'.decode('hex')
'\xfa\xfb\xfc\xfd'
>>> '31323334'.decode('hex')
'1234'

In Python3 you can use bytes.fromhex()

>>> bytes.fromhex('01')
b'\x01'
>>> bytes.fromhex('0102030405')
b'\x01\x02\x03\x04\x05'
>>> bytes.fromhex('fafbfcfd')
b'\xfa\xfb\xfc\xfd'
>>> bytes.fromhex('31323334')
b'1234'

If you wish to convert to a str do it the usual way with whichever encoding you are using

>>> bytes.fromhex('31323334').decode('utf-8')
'1234'