code: def parse_dsn(dsn_string):
      
      dsn = urlparse(dsn_string)
      scheme = dsn.scheme.split('+')[0]
      username = password = host = port = None
      host = dsn.netloc
      if '@' in host:
          username, host = host.split('@')
          if ':' in username:
              username, password = username.split(':')
              password = unquote(password)
          username = unquote(username)
      if ':' in host:
          host, port = host.split(':')
          port = int(port)
      database = dsn.path.split('?')[0][1:]
      query = dsn.path.split('?')[1] if '?' in dsn.path else dsn.query
      kwargs = dict(parse_qsl(query, True))
      if scheme == 'sqlite':
          return SQLiteDriver, [dsn.path], {}
      elif scheme == 'mysql':
          kwargs['user'] = username or 'root'
          kwargs['db'] = database
          if port:
              kwargs['port'] = port
          if host:
              kwargs['host'] = host
          if password:
              kwargs['passwd'] = password
          return MySQLDriver, [], kwargs
      elif scheme == 'postgresql':
          kwargs['user'] = username or 'postgres'
          kwargs['database'] = database
          if port:
              kwargs['port'] = port
          if 'unix_socket' in kwargs:
              kwargs['host'] = kwargs.pop('unix_socket')
          elif host:
              kwargs['host'] = host
          if password:
              kwargs['password'] = password
          return PostgreSQLDriver, [], kwargs
      else:
          raise ValueError('Unknown driver %s' % dsn_string)
docs: Parse a connection string and return the associated driver