Begin a new payment session. Searches wallet for an account that's
        marked as available and has a 0 balance. If one is found, the account
        number is returned and is marked as unavailable. If no account is
        found, a new account is created, placed in the wallet, and returned.

        :param wallet: Wallet to begin payment in
        :type wallet: str

        :raises: :py:exc:`nano.rpc.RPCException`

        >>> rpc.payment_begin(
        ... wallet="000D1BAEC8EC208142C99059B393051BAC8380F9B5A2E6B2489A277D81789F3F"
        ... )
        "xrb_3e3j5tkog48pnny9dmfzj1r16pg8t1e76dz5tmac6iq689wyjfpi00000000"

def payment_begin(self, wallet):
        """
        Begin a new payment session. Searches wallet for an account that's
        marked as available and has a 0 balance. If one is found, the account
        number is returned and is marked as unavailable. If no account is
        found, a new account is created, placed in the wallet, and returned.

        :param wallet: Wallet to begin payment in
        :type wallet: str

        :raises: :py:exc:`nano.rpc.RPCException`

        >>> rpc.payment_begin(
        ... wallet="000D1BAEC8EC208142C99059B393051BAC8380F9B5A2E6B2489A277D81789F3F"
        ... )
        "xrb_3e3j5tkog48pnny9dmfzj1r16pg8t1e76dz5tmac6iq689wyjfpi00000000"

        """

        wallet = self._process_value(wallet, 'wallet')

        payload = {"wallet": wallet}

        resp = self.call('payment_begin', payload)

        return resp['account']