使用Try-and-Except块，但在Except部分，它表示未定义Python

我的代码是把华氏温度转换成摄氏温度。就是这样

def again():
    calc = raw_input("Press y to convert again. Press n to quit. ").lower()
    if calc == "y":
        main()
    elif calc == "n":
        quit()
    else:
        again()

def main():
    fahrenheit = input("What do you want to convert from Fahrenheit to Celsius? ")
    try:
        celsius = (fahrenheit - 32) *5 / float(9) 
        print('%0.2F degree Celsius is equal to about %0.1f degree Fahrenheit' %(celsius,fahrenheit))
        again()
    except ValueError:
        print("That is not a number")
        check()

如果运行它，请键入要转换的字母而不是数字。它不执行Except位，但表示未定义字母。如果我有

---

fahrenheit=input（“您想将什么温度从华氏温度转换为摄氏温度？”）

，如何使用Try位将引号中的数字转换为不带引号的正常数字？我想这是因为我选择了

值错误

，但我不知道。任何帮助都将不胜感激

您使用的是python 2.x，而不是3.x。在Python2.x中，您需要使用

raw\u input

，而不是

input

。因此，改变这一点：

fahrenheit = input(
    "What do you want to convert from Fahrenheit to Celsius? ")

为此：

fahrenheit = raw_input(
    "What do you want to convert from Fahrenheit to Celsius? ")

运行时显示python 2.7中的

input（）

失败：

C:\Python27\python.exe test.py
What do you want to convert from Fahrenheit to Celsius? d
Traceback (most recent call last):
  ...
    "What do you want to convert from Fahrenheit to Celsius? ")
  File "<string>", line 1, in <module>
NameError: name 'd' is not defined

"C:\Program Files (x86)\Python35-32\python.exe" test.py
What do you want to convert from Fahrenheit to Celsius? d
Traceback (most recent call last):
  ...
  File "C:/Users/stephen/Documents/src/testcode/test.py", line 31, in main
    celsius = (fahrenheit - 32) * 5 / float(9)
TypeError: unsupported operand type(s) for -: 'str' and 'int'

C:\Python27\python.exe test.py awk_data.txt
What do you want to convert from Fahrenheit to Celsius? d
Traceback (most recent call last):
...
  File "C:/Users/stephen/Documents/src/testcode/test.py", line 31, in main
    celsius = (fahrenheit - 32) * 5 / float(9)
TypeError: unsupported operand type(s) for -: 'str' and 'int'

运行显示

原始输入（）

使用python 2.7:

C:\Python27\python.exe test.py
What do you want to convert from Fahrenheit to Celsius? d
Traceback (most recent call last):
  ...
    "What do you want to convert from Fahrenheit to Celsius? ")
  File "<string>", line 1, in <module>
NameError: name 'd' is not defined

"C:\Program Files (x86)\Python35-32\python.exe" test.py
What do you want to convert from Fahrenheit to Celsius? d
Traceback (most recent call last):
  ...
  File "C:/Users/stephen/Documents/src/testcode/test.py", line 31, in main
    celsius = (fahrenheit - 32) * 5 / float(9)
TypeError: unsupported operand type(s) for -: 'str' and 'int'

C:\Python27\python.exe test.py awk_data.txt
What do you want to convert from Fahrenheit to Celsius? d
Traceback (most recent call last):
...
  File "C:/Users/stephen/Documents/src/testcode/test.py", line 31, in main
    celsius = (fahrenheit - 32) * 5 / float(9)
TypeError: unsupported operand type(s) for -: 'str' and 'int'

---

执行

华氏-32

时，代码试图从字符串中减去整数，这会导致此异常：

TypeError: unsupported operand type(s) for -: 'str' and 'int'

这不是

ValueError

，因此它不会被

except

子句捕获

---

如果要捕获

ValueError

，需要将

fahrenheit=int（fahrenheit）

放入

try:

块中。

将用户输入转换为整数，如下所示：

fahrenheit = int(fahrenheit)

如果您使用的是Python3.x，那么这应该是您的最终代码

def again():
calc = input("Press y to convert again. Press n to quit. ").lower()
if calc == "y":
    main()
elif calc == "n":
    quit()
else:
    again()

def main():
fahrenheit = input("What do you want to convert from Fahrenheit to Celsius? ")
try:
    fahrenheit = int(fahrenheit)
    celsius = (fahrenheit - 32) *5 / float(9) 
    print('%0.2F degree Celsius is equal to about %0.1f degree Fahrenheit' %(celsius,fahrenheit))
    again()
except ValueError:
    print("That is not a number")
    #check()
main()

---

希望有帮助

请显示您收到的错误。您的代码将生成ValueError，但如果传递一个字母，则不会捕获ValueError。它会生成ValueError。我只是检查一下。是的，是的，但不在

try

内，这样它就不会被抓到并打印“那不是一个数字”。