from binascii import crc32

def get_checksum(phrase):
    """Given a mnemonic word string, return a string of the computed checksum.
   :rtype: str
   """
    phrase_split = phrase.split(" ")
    phrase = phrase_split[:24]
    wstr = "".join(word[:3] for word in phrase)
    wstr = bytearray(wstr.encode('utf-8'))
    z = ((crc32(wstr) & 0xffffffff) ^ 0xffffffff ) >> 0
    z2 = ((z ^ 0xffffffff) >> 0) % len(phrase)
    return phrase_split[z2]