code: def totp(key, t, digits=6, step=30):
      
      return hotp(key, T(t, step), digits)
docs: These test vectors come from RFC-6238
      (https://tools.ietf.org/html/rfc6238#appendix-B).
      >>> import datetime
      >>> key = b'12345678901234567890'
      >>> totp(key, datetime.datetime.fromtimestamp(59), digits=8)
      '94287082'
      >>> totp(key, datetime.datetime.fromtimestamp(1111111109), digits=8)
      '07081804'
      >>> totp(key, datetime.datetime.fromtimestamp(20000000000), digits=8)
      '65353130'