如何解决 Python 中的 KeyError？

Question

我正在尝试创建一个预测工具，用于分析给定机场的历史客流量。分析将基于与机场相关国家的各种 GDP（国内生产总值）的线性回归。一个人可以输入独立变量的名称，然后从 Excel 文件中选择该名称。一旦有人收到“您希望将哪个国家的 GDP 设置为回归分析的自变量？”的问题，就有可能输入错误的国家/地区。在那种情况下，我会收到一个 KeyError。我正在尝试使用“try / except”来解决这个问题，但我仍然收到 KeyError（参见第 36-49 行）。我真的很感激一些帮助！谢谢！如果有帮助，这里是 GitHub 链接：https ://github.com/DR7777/snowflake （参见 main_file.py 的第 36-49 行）这是我的代码：我试过使用while循环，for / except，但似乎我太新了，无法理解。# This part saves the first row of the Excel as a list,# so I can give the user a list of all the countries, # if the person types in a country, that's not on the list.loc = ("IMF_Country_GDP_Data.xlsx") wb = xlrd.open_workbook(loc) sheet = wb.sheet_by_index(0) sheet.cell_value(0, 0) list_of_countries = sheet.row_values(0)possible_selection = (list_of_countries[1:]) #This is the list with all the possible countries, without the Excel cell A1#Introductionprint("Hello, welcome to the Air Traffic Forecasting Tool V0.1!")print("Which Country's GDP would you like to set as the independant variable for the Regression Analysis?")Country_GDP = input("Please type your answer here: ")#here we check, if the typed Country is in the listtry:    possible_selection == Country_GDP    print("Your country is on the list.")except KeyError:    print("Oh no! You typed a country, which is not in our database!")    print("Please select one of the countries listed below and try again")    print(possible_selection)#now continuing with the previous codeprint("Ok, I will conduct the analysis based on the GDP of " + str(Country_GDP) + "!")print("Here are your results: ")#here is the rest of the code我想要实现的是：如果一个人输入了一个国家列表中的名字，程序就会运行回归。如果该国家/地区不在列表中，我不想收到 KeyError。我想让程序说：哦不！您输入的国家/地区不在我们的数据库中！请选择下面列出的国家之一，然后再试一次，然后打印 possible_selection 变量，这样用户就可以看到他有哪个选项。

Answer 1

根本不需要得到关键错误。只需使用in.

while True:

    selection = input('Which country?')

    if selection in list_of_countries: 

        print('Your country is on the list')

        break

    else:

        print('You typed an invalid entry, lets try again')