undefined function error

[JonWayn]

from scrapy import Spider
from scrapy.http import Request


class TesterSpider(Spider):
    name = 'tester'
    allowed_domains = ['books.toscrape.com']
    start_urls = ['http://books.toscrape.com/']


    def parse(self, response):
        books = response.xpath("//h3/a/@href").extract()
        for book in books:
            absolute_url = response.urljoin(book)
            yield Request(absolute_url, callback=self.parse_book)

        # process next page
        next_page_url = response.xpath("//a[text()='next']/@href").extract_first()
        absolute_next_page_url = response.urljoin(next_page_url)
        yield Request(absolute_next_page_url)


    def parse_book(self, response):
        title = response.xpath("//h1/text()").extract_first()
        price = response.xpath("//*[@class='price_color']/text()").extract_first()
        img_url = response.xpath("//img/@src").extract_first()
        img_url = img_url.replace('../..', 'https://books.toscrape.com')
        rating = response.xpath("//p[starts-with(@class,'star-rating')]/@class").extract_first()
        rating = rating.replace('star-rating ', '')
        desc = response.xpath("//div[(@id='product_description')]/following-sibling::p/text()").extract_first()
        
        # Product Description
        upc = product_desc(response, 'UPC')
        product_type = product_desc(response, 'Product Type')
        availability = product_desc(response, 'Availability')
        number_of_reviews = product_desc(response, 'Number of reviews')

        yield{
            'Title': title,
            'Price': price,
            'Location': img_url,
            'Rating': rating,
            'Description': desc,
            'UPC': upc,
            'Product Type': product_type,
            'Availability': availability,
            'Reviews': number_of_reviews
        }


    def product_desc(response, lookup):
        return response.xpath("//th[text()='" + lookup + "']/following-sibling::td/text()").extract_first()

As you can see, at the very bottom, the function 'product_desc' is defined, but just above that where I called it just above the yield block, my IDE, VS Code reports that it is undefined. Can anyone spot what I am missing.

Thank you