EncoderDecoder.py

# Code is based off of forum post from user "vegaseat" on http://www.daniweb.com/software-development/python/threads/63552

def choice():
    print '1) Encrypt Text';
    print '2) Decrypt Text';
    print '3) Exit';

    choose = input("Enter Choice: ");

    if choose == 1:
        En();
    elif choose == 2:
        De();
    elif choose == 3:
        print 'Bye!';
    else:
        print 'Enter valid choice.';
        print;
        choice();


def En():
    str1 = raw_input("Enter text to be encoded: ");
    encodedstr1 = str1.encode('rot13');
    encodedstr2 = list(encodedstr1)
    encodedstr2.reverse()
    encodedstr2[0:] = [''.join(encodedstr2[0:])]
    print "Encoded text: ", encodedstr2;
    print;
    raw_input("Press <Enter>");
    print;
    choice();



def De():
    str1 = raw_input("Enter text to be decoded: ");
    decodedstr1 = str1.encode('rot13');
    decodedstr2 = list(decodedstr1);
    decodedstr2.reverse();
    decodedstr2[0:] = [''.join(decodedstr2[0:])];
    print "Decoded text: ", decodedstr2;
    print;
    raw_input("Press <Enter>");
    print;
    choice();

On line 27 and 41, you don't actually need to use [0:], you can do [:] and it will still work - the 0 is assumed, if you don't put anything in.