Question

我想从列表中获取两个值，然后添加它们。我想用try和except块来做。皮查姆没有问题。但是输出不显示任何内容或显示“无”。这是代码：

def tryint():
    global mylist
    try:
        mylist = list[map(int, mylist)]
        ans = mylist[0] + mylist[1]
        return ans

    except:
        pass

a = input('First value: ')
b = input('Second value: ')
mylist = [a, b]
tryint()

我尝试将tryint()更改为print(tryint())，但随后仅显示"None"。也没有错误消息。

Answer 1

我将以您的代码作为我们如何改进代码的起点

首先解决您的问题

# What you are trying to do is supply two parameters 
# this is better accomplished by supplying the parameters  
def tryint():                            
    global mylist            
    try:
        # As mentioned list is a method call so you need to use ()
        mylist = list[map(int, mylist)]
        # Try to only put the code you suspect might cause an exception
        # in your try/except block.
        ans = mylist[0] + mylist[1]
        return ans

    # Always provide the exception you are expecting or at least `Exception`
    # If your code isn't going to handle the exception don't handle it.
    except:
        pass

a = input('First value: ')
b = input('Second value: ')
mylist = [a, b]
tryint()

下一步，让我们改善您的原始解决方案

# The function now excepts two parameters
def try_int(a, b):
    try:
        # Only type conversion is in the try block
        a = int(a)
        b = int(b)
    # Only ValueError and TypeError are handled
    except (ValueError, TypeError):
        return None

    # At this point we can assume we have integers and safely
    # do the addition.
    return a + b

a = input("First value: ")
b = input("Second value: ")
print(try_int(a, b))

现在，我们传入输入并仅解析输入的期望值。

但是，我们可以通过立即向您的用户提供反馈来做得更好。

def input_int(msg):
    # Keep trying until a valid value is added
    while True:
        value = input(msg)

        # Allow the user an out be entering nothing
        if not value:
            return None

        try:
            # Return a valid value
            return int(value)
        except ValueError:
            # Provide feedback
            print("Expected an integer value, please try again")

a = input_int("First value: ")
if a is None:
    exit()

b = input_int("Second value: ")
if b is None:
    exit()

# At this point we know we have two integers
print(a + b)

Answer 2

有很多方法可以完成您正在做的事情，但是我将向您展示出错的地方：-

def tryint():
    global mylist
    try:
        mylist = list(map(int, mylist))   # Here you have to use parrenthesis instead of square brackets.
        ans = mylist[0] + mylist[1]
        return ans

    except Exception as e:  # This is how you write exception handling.
        pass

a = input('First value: ')
b = input('Second value: ')
mylist = [a, b]
tryint()

输出

First value: 5
Second value: 4
9

函数未从列表中获取值

2 个答案: