问Python：“如果i.find('a')['id']不是无：”返回TypeError 'NoneType‘对象不可订阅，但是print()返回一个值

EN

import requests
from bs4 import BeautifulSoup


def average(price_list):
    return sum(price_list) / len(price_list)


# Requests search data from Website
page_link = 'URL'
page_response = requests.get(page_link, timeout=5)  # gets the webpage (search) from Website
page_content = BeautifulSoup(page_response.content, 'html.parser')  # turns the webpage it just retrieved into a BeautifulSoup-object

# Selects the product listings from page content so we can work with these
product_listings = page_content.find_all("div", {"class": "unit flex align-items-stretch result-item"})

prices = []  # Creates a list to add the prices to
uids = [] # Creates a list to store the unique ids

for product in product_listings:

## UIDS 
    if product.find('a')['id'] is not None:
        uid = product.find('a')['id']
        uids.append(uid)

# PRICES
    if product.find('p', class_ = 'result-price man milk word-break') is not None:# assures that the loop only finds the prices
        price = int(product.p.text[:-2].replace(u'\xa0', ''))  # makes a temporary variable where the last two chars of the string (,-) and whitespace are removed, turns into int
        prices.append(price)  # adds the price to the list