如何在xpath中传递两个不同的参数？

<bookstore>
  <book>
    <title>Book 1</title>
    <author>Author 1</author>
  </book>
  <book>
    <title>Book 2</title>
    <author>Author 2</author>
  </book>
</bookstore>

//book[title=$title and author=$author]

from lxml import etree

# 创建XML文档对象
xml = '''
<bookstore>
  <book>
    <title>Book 1</title>
    <author>Author 1</author>
  </book>
  <book>
    <title>Book 2</title>
    <author>Author 2</author>
  </book>
</bookstore>
'''
doc = etree.fromstring(xml)

# 定义参数值
title_param = "Book 1"
author_param = "Author 1"

# 定义XPath表达式
xpath_expr = "//book[title=$title and author=$author]"

# 设置参数值
ns = {"title": title_param, "author": author_param}

# 执行XPath查询
result = doc.xpath(xpath_expr, namespaces=ns)

# 输出结果
for book in result:
    print(etree.tostring(book).decode())