<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def find(self, substring):
        '''
        byte-like -> int
        Finds the index of substring
        '''
        if isinstance(substring, ByteData):
            substring = substring.to_bytes()
        return self._bytes.find(substring)