How to use the asttokens.util.expect_token function in asttokens

def handle_comp(self, open_brace, node, first_token, last_token):
    # For list/set/dict comprehensions, we only get the token of the first child, so adjust it to
    # include the opening brace (the closing brace will be matched automatically).
    before = self._code.prev_token(first_token)
    util.expect_token(before, token.OP, open_brace)
    return (before, last_token)

def handle_attr(self, node, first_token, last_token):
    # Attribute node has ".attr" (2 tokens) after the last child.
    dot = self._code.find_token(last_token, token.OP, '.')
    name = self._code.next_token(dot)
    util.expect_token(name, token.NAME)
    return (first_token, name)

def visit_keyword(self, node, first_token, last_token):
    if node.arg is not None:
      equals = self._code.find_token(first_token, token.OP, '=', reverse=True)
      name = self._code.prev_token(equals)
      util.expect_token(name, token.NAME, node.arg)
      first_token = name
    return (first_token, last_token)