Python: How to decode uuencoded text

Question

I've been reading about uuencoding and was wondering how to decode the following example given in this link using Python.

https://en.wikipedia.org/wiki/Uuencoding

Original text: Cat

Uuencoded text: #0V%T

Python 2

$ python -c 'print "Cat".encode("uu")'
begin 666 <data>
#0V%T

end

$

Python 3

$ python3 -c "from codecs import encode;print(encode(b'Cat', 'uu'))"
b'begin 666 <data>\n#0V%T\n \nend\n'
$

Answer 1

It is just the inverse of the original function....

Let me try and show you. I will use 2 common encoding type uu and base-64.

Python 3

from codecs import decode,encode
import uu

orig="Cat"
encoding_types=['uu','base-64']
for et in encoding_types:
    enc_data=encode(orig.encode(),et)
    un_enc_data=decode(enc_data,et)
    print("\n\nEncoding  : {}".format(et))
    print("Orig          : {}".format(orig))
    print("Encoded       : {}".format(enc_data))
    print("byte UnEncoded: {}".format(un_enc_data))
    print("utf8 UnEncoded: {}".format(un_enc_data.decode()))

This should output

Encoding  : uu
Orig          : Cat
Encoded       : b'begin 666 <data>\n#0V%T\n \nend\n'
byte UnEncoded: b'Cat'
utf8 UnEncoded: Cat


Encoding  : base-64
Orig          : Cat
Encoded       : b'Q2F0\n'
byte UnEncoded: b'Cat'
utf8 UnEncoded: Cat

We need the final .decode() as we initially converted the str data object into bytes with the encode().

Answer 2

The library uu is now deprecated.

See here and here. Even codecs relies on uu. See here.

You should use binascii:

c="02&DA($AO=R!A<F4@>6]U/P``"
 
import binascii
m = binascii.a2b_uu(c)
print(m)

Then you can read:

Hi! How are you?

.

You might need to implement uu encoding alone or to choose another library.

To write your own library, do:

def get_bits(num, start, end, length=64):
    mask = 2**(end-start)-1
    shift = length - (end-start) - start

    return (num & (mask << shift)) >> shift


def decode_uu_charset(cipher_text):
        plain_text = ""

        three_characters = []
        for character_group in list(zip(*[iter(cipher_text[1:len(cipher_text)])] * 4)):
            character_group = "".join(character_group)
            four_six_bits = []
            for c in character_group:
                c = bin((ord(c) - 32) % 64)[2:].zfill(6)
                four_six_bits.append(c)
            three_characters.append(
                chr(int(str(bin(get_bits(int(four_six_bits[0], 2), 0, 6, 6))[2:].zfill(6)) +
                str(bin(get_bits(int(four_six_bits[1], 2), 0, 2, 6))[2:].zfill(2)), 2))
            )
            three_characters.append(
                chr(int(str(bin(get_bits(int(four_six_bits[1], 2), 2, 6, 6))[2:].zfill(4)) +
                str(bin(get_bits(int(four_six_bits[2], 2), 0, 4, 6))[2:].zfill(4)), 2))
            )
            three_characters.append(
                chr(int(str(bin(get_bits(int(four_six_bits[2], 2), 4, 6, 6))[2:].zfill(2)) +
                str(bin(get_bits(int(four_six_bits[3], 2), 0, 6, 6))[2:].zfill(6)), 2))
            )
        for c in three_characters:
            if ord(c) != 0:
                plain_text += c

        return plain_text


plain_text = decode_uu_charset("02&DA($AO=R!A<F4@>6]U/P``")
print(plain_text)

You should read

Hi! How are you?

.