A string is encoded with six of the most popular letters of the English language switched when the word "encode" precedes the string. Otherwise, the string is decoded when "decode" precedes the string and the six letters are switched back to their original state.

SpyCoder

def  spy_coder(input):
    encode = ''
    decode = ''
    result_input = input.split()
    del result_input[0]
    result_input = " ".join(result_input)
    if 'encode' in input:
        print 'encoding...'
        for letter in result_input:
            if letter == 't':
                encode += 'e'
            elif letter == 'a':
                encode += 't'
            elif letter == 'o':
                encode += 'a'
            elif letter == 'i':
                encode += 'o'
            elif letter == 'n':
                encode += 'i'
            elif letter == 'e':
                encode += 'n'
            elif letter == 'T':
                encode += 'E'
            elif letter == 'A':
                encode += 'T'
            elif letter == 'O':
                encode += 'A'
            elif letter == 'I':
                encode += 'O'
            elif letter == 'N':
                encode += 'I'
            elif letter == 'E':
                encode += 'N'
            else:
                encode += letter
        return encode
    elif 'decode' in input:
        print 'decoding...'
        for letter in result_input:
            if letter == 'e':
                decode += 't'
            elif letter == 't':
                decode += 'a'
            elif letter == 'a':
                decode += 'o'
            elif letter == 'o':
                decode += 'i'
            elif letter == 'i':
                decode += 'n'
            elif letter == 'n':
                decode += 'e'
            elif letter == 'E':
                decode += 'T'
            elif letter == 'T':
                decode += 'A'
            elif letter == 'A':
                decode += 'O'
            elif letter == 'O':
                decode += 'I'
            elif letter == 'I':
                decode += 'N'
            elif letter == 'N':
                decode += 'E'
            else:
                decode += letter
        return decode