<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _read_mode_mptcp(self, size, kind):
 """Read Multipath TCP option. Positional arguments: * size - int, length of option * kind - int, 30 (Multipath TCP) Returns: * dict -- extracted Multipath TCP (MP-TCP) option Structure of MP-TCP [RFC 6824]: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 | Kind | Length |Subtype| | | Subtype-specific data | | (variable length) | Octets Bits Name Description 0 0 tcp.mp.kind Kind (30) 1 8 tcp.mp.length Length 2 16 tcp.mp.subtype Subtype 2 20 tcp.mp.data Subtype-specific Data """

        bins = self._read_binary(1)
        subt = int(bins[:4], base=2)    # subtype number
        bits = bins[4:]                 # 4-bit data
        dlen = size - 1                 # length of remaining data

        # fetch subtype-specific data
        func = mptcp_opt.get(subt)
        if func is None:    # if subtype not exist, directly read all data
            temp = self._read_fileng(dlen)
            data = dict(
                kind=kind,
                length=size,
                subtype='Unknown',
                data=bytes(chr(int(bits[:4], base=2)), encoding='utf-8') + temp,
            )
        else:               # fetch corresponding subtype data dict
            data = func(self, bits, dlen, kind)
        return data