CODEWITHSUNDEEP
python
Mark Irvine
Mark Irvine

Reputation: 1369

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

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()

Upvotes: 2

Views: 9774

Answers (4)

John La Rooy
John La Rooy

Reputation: 304355

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'

Upvotes: 4

alexis
alexis

Reputation: 50220

You mean like this?

def ascii_to_packed_hex(s):
    return "".join(chr(int(s[n:n+2], 16)) for n in range(0,len(s), 2))

Upvotes: 1

agf
agf

Reputation: 176910

If you can't use binascii or str.decode('hex') because this is homework or something, you can:

def ascii_to_packed_hex(string_data): 
    # convert each pair of hex digits in the string into an integer
    # then convert those to characters and join them into a string
    return ''.join(chr(int(digits, 16)) for digits in 
                (string_data[x:x+2] for x in range(0, len(string_data), 2)))

Upvotes: 2

mechanical_meat
mechanical_meat

Reputation: 169424

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()

Upvotes: 4

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