<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def import_keybase(useropt):
 """Imports a public GPG key from Keybase"""

    public_key = None
    u_bits = useropt.split(':')
    username = u_bits[0]
    if len(u_bits) == 1:
        public_key = cryptorito.key_from_keybase(username)
    else:
        fingerprint = u_bits[1]
        public_key = cryptorito.key_from_keybase(username, fingerprint)

    if cryptorito.has_gpg_key(public_key['fingerprint']):
        sys.exit(2)

    cryptorito.import_gpg_key(public_key['bundle'].encode('ascii'))
    sys.exit(0)