访问非空列表中的第一个元素时导致IndexError的原因是什么?

Question

如果这太简单，请原谅我，我才刚刚开始学习编程。

任务:

从API调用创建天气报告。询问城市，从网页上查找城市，并返回未来五天的天气预报。然后再次请求一个城市，直到按下CTRL-C。

• 这个我已经做了，它工作没有问题。

在此基础上，如果请求的城市名称没有退出，则再次请求城市名称

• 这里我有一个问题与我的代码，当我要求一个不存在的城市，它确实要求一个新的城市，我可以键入一个现有的城市，获得天气关系融洽，但然后不是要求下一个城市名称，它打破了代码与以下错误:

City?
> fhusi
City not found
City?
> London
Here is the weather in London
2021-01-22: Heavy Cloud 6.2°C
2021-01-23: Heavy Cloud 3.8°C
2021-01-24: Heavy Rain 3.5°C
2021-01-25: Light Rain 3.8°C
2021-01-26: Showers 4.5°C

Traceback (most recent call last):
File "weather.py", line 45, in <module>
main()
File "weather.py", line 32, in main
city = search_city(query)
File "weather.py", line 19, in search_city
return seach_response[0]
IndexError: list index out of range

这是我的代码:是的，里面有很多注释，这就是我如何记住我的错误

# pylint: disable=missing-docstring
import sys
import urllib.parse
import requests
BASE_URI = "https://www.metaweather.com"

def search_city(query):
# : Look for a given city and disambiguate between several candidates. Return one city (or None)
seach_response = requests.get("https://www.metaweather.com/api/location/search/?query="+query).json() # [0] return results as dict format
# print(requests.get("https://www.metaweather.com/api/location/search/?query="+query).json)
# print(seach_response.status_code) --> remember to remove .json() from seach to see status code
# if seach_response.status_code != 200: --> didn't work, as a empty list is returned if city doesn't exit and not an error code
if seach_response == []:
print("City not found")
main()
return seach_response[0]

def weather_forecast(woeid):
# : Return a 5-element list of weather forecast for a given woeid
weather_response = requests.get(f'https://www.metaweather.com/api/location/{woeid}/').json()
#print(weather_response) --use https://jsonformatter.curiousconcept.com/# to see the data nicely and pick relevant data
weather = weather_response['consolidated_weather'][:5]
return weather

def main():
query = input("City?n> ")
city = search_city(query)
#print(city) --control of code
woeid = city['woeid']
forecast = weather_forecast(woeid)
# : Display weather forecast for a given city
print(f"Here is the weather in {city['title']}")
for predition in forecast:
print(f"{predition['applicable_date']}: {predition['weather_state_name']} {round(predition['the_temp'],1)}N{DEGREE SIGN}C")

if __name__ == '__main__':
try:
while True:
main()
except KeyboardInterrupt:
print('nGoodbye!')
sys.exit(0)

Answer 1

问题在于您的search_city(query)函数。请看下面几行:

if seach_response == []: # empty list
print("City not found")
main() # Execute main again
# Opps, main has executed and the function is still going
# but searc_response is an empty list so search_response[0] is going to be out of bounds
return seach_response[0]

要解决上述问题，您需要return main()而不是main()。在main之后，您应该检查search_city(query)是否返回None。

所以你的代码应该是这样的

def search_city(query):
seach_response = requests.get("https://www.metaweather.com/api/location/search/?query="+query).json() # [0] return results as dict format
if seach_response == []:
print("City not found")
return main() # return
return seach_response[0]

和

def main():
query = input("City?n> ")
city = search_city(query)
if city is None: 
return
woeid = city['woeid'] # here if city is None it will throw an exception
forecast = weather_forecast(woeid)
print(f"Here is the weather in {city['title']}")
for predition in forecast:
print(f"{predition['applicable_date']}: {predition['weather_state_name']} {round(predition['the_temp'],1)}N{DEGREE SIGN}C")