Python Try / Except

Question

使用Try / Except的正确方法是什么？

我是Python的新手，只是想学习这种新技术，所以任何想法为什么这不起作用？

temp=input("Please choose an option: ")
try:
    if temp == ("1"):
        fc=input("Fahrenheit: ")
        fer(int(fc))
    if temp == ("2"):
        cf=input("Celsius: ")
        cel(int(cf))
except ValueError:
    print("It looks like you input a value that wasn't a number!")

如果你把“temp”中的值设置为不是1或2而不是它应该打印出来的那么它不是数字但是没有，那么有什么想法吗？

Answer 1

“看起来您输入的值不是数字！”将在您的try块中出现异常时打印。你想做的是：

temp=input("Please choose an option: ")
try:
    if temp == ("1"):
        fc=input("Fahrenheit: ")
        fer(int(fc))
    elif temp == ("2"):
        cf=input("Celsius: ")
        cel(int(cf))
    else:
        print("It looks like you input a value that wasn't 1 or 2!")
except ValueError:
    print("It looks like you input a value that wasn't a number!")

你必须保持try和catch，因为输入可能不是数字。

Answer 2

temp=input("Please choose an option: ")
try:
    if temp == ("1"):   # is temp == "1"
        fc=input("Fahrenheit: ") # if yes, get number
        fer(int(fc))  # convert to int, this can raise an exception
    if temp == ("2"):  # is temp == "2"
        cf=input("Celsius: ")  # if yes, get number
        cel(int(cf))  # this can raise an exception
except ValueError:   # capture all ValueError exceptions
    print("It looks like you input a value that wasn't a number!")

temp的值永远不会在您的代码中引发异常（只有输入的解析可以），所以它只是通过。您需要手动添加检查以确保temp是有效条目之一。

更好的方法是（并且您可以通过例外验证temp）：

def handle_f():
   fc=input("Fahrenheit: ") # if yes, get number
   fer(int(fc))  # convert to int, this can raise an exception

def handle_C():
    cf=input("Celsius: ")  # if yes, get number
    cel(int(cf))  # this can raise an exception   

fun_dict = {"1": handle_f, "2": handle_c}

try:
   fun_dict[temp]()
except KeyError: # handle temp not being valid
    print('not a valid temperature type')
except ValueError:
    print("It looks like you input a value that wasn't a number!")

Answer 3

我认为从用户那里抽象读取int的过程更简洁：

def input_int(prompt):
    try:
        return int(input(prompt))
    except ValueError:
        print("It looks like you input a value that wasn't a number!")

temp=input("Please choose an option: ")
if temp == ("1"):
    fc=input_int("Fahrenheit: ")
    fer(fc)
if temp == ("2"):
    cf=input_int("Celsius: ")
    cel(cf)