请问为什么这段代码运行时会说有r不能用？

Question

url = ("http://flights.ctrip.com/domesticsearch/search/SearchFirstRouteFlights?DCity1={}&ACity1={}&SearchType=S&DDate1={}").format(DCity1,ACity1,DDate1)
    try:
        r = requests.get(url,headers = headers,verify=False)
    except Exception as e:
        print(repr(e))
    print(url)
    airline_tickets = r.json()['fis']
    TrainsCollection(airline_tickets).pretty_print()

Answer 1

那是因为前面没有获取到r 值，或r值为空，或get到的数据不是json格式。