How to use the installer.payload.sgh_scratch.ScratchError function in installer

def connect(self):
        """
        Connects to Scratch.
        """
        self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        try:
            self.socket.connect((self.host, self.port))
        except socket.error as e:
            self.connected = False
            raise ScratchError(e)
        self.connected = True

def _write(self, data):
        """
        Writes string data out to Scratch
        """
        total_sent = 0
        length = len(data)
        while total_sent < length:
            try:
                sent = self.socket.send(data[total_sent:].encode('UTF-8'))
            except socket.error as e:
                self.connected = False
                raise ScratchError(e)
            if sent == 0:
                self.connected = False
                raise ScratchConnectionError("Connection broken")
            total_sent += sent

import array
import itertools
import socket
import struct
import sys

# For Scratch 3 handle long as int 
if sys.version > '3':
    long = int

class ScratchError(Exception): pass
class ScratchConnectionError(ScratchError): pass        

class Scratch(object):

    prefix_len = 4
    broadcast_prefix_len = prefix_len + len('broadcast ')
    sensorupdate_prefix_len = prefix_len + len('sensor-update ')

    msg_types = set(['broadcast', 'sensor-update'])

    def __init__(self, host='localhost', port=42001):
        self.host = host
        self.port = port
        self.socket = None
        self.connected = False
        self.connect()

def _read(self, size):
        """
        Reads size number of bytes from Scratch and returns data as a string
        """
        data = b''
        while len(data) < size:
            try:
                chunk = self.socket.recv(size-len(data))
            except socket.error as e:
                self.connected = False
                raise ScratchError(e)
            if chunk == '':
                self.connected = False
                raise ScratchConnectionError("Connection broken")
            data += chunk
        return data