input: Write a python function to extract temperature values from a given URL using requests and BeautifulSoup.
  assert extract_temperatures('https://www.wunderground.com/history/airport/KMYF/2017/12/20/DailyHistory.html?req_city=San+Diego&req_state=CA&req_statename=California') != []
  assert isinstance(extract_temperatures('https://www.wunderground.com/history/airport/KMYF/2017/12/20/DailyHistory.html?req_city=San+Diego&req_state=CA&req_statename=California'), list)
  assert all(isinstance(temp, str) for temp in extract_temperatures('https://www.wunderground.com/history/airport/KMYF/2017/12/20/DailyHistory.html?req_city=San+Diego&req_state=CA&req_statename=California'))
output: def extract_temperatures(url):
      import requests
      from bs4 import BeautifulSoup
      
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
      
      temperatures = []
      for temp in soup.find_all('span', class_='wu-value wu-value-to'):
          temperatures.append(temp.text)
      
      return temperatures