python - 不使用 max() 打印列表中的最大数字

Question

当用户输入无效值存储到“number”变量中时，我无法防止脚本崩溃。

程序用途:允许用户输入整数，将它们存储到列表中，然后查找并打印最大的数字。不允许在输入中使用字符串或 float 。

功能:

1. getNum(prompt) - 测试输入值并将其转换为整数并返回 y。
2. swap(A, x, y) - 用于对数据进行排序的简单交换例程函数。 (当前未使用)
3. sortNum(A) - 排序并使用列表中的交换例程。
4. maxIt(numbers) - 查找列表中最大的数字。 (使用中)，如果我使用这个 max 函数，我认为我什至不需要对列表进行排序。
5. main()

代码:

def getNum(prompt):
    # Function to call when asking for the numbers later.
    # Try/except to catch crashes if failing to store integer.
    try:
        x = input(prompt)
        y = int(x)
        return y

    # Message to print when excepting.
    except:
        print("I was expecting an integer number, please try again... \n")


# Function to swap to highest # in list 'numbers'.
def swap(A, x, y):
    temp1 = A[x]
    A[x] = A[y]
    A[y] = temp1

# Function to perform the looping/swap routine.
# Program can find max with separate function.
## This function is to sort the numbers in the list.
def sortNum(A):
    for i in range(len(A)):
        for k in range(len(A) - 1):
            first = k
            second = k + 1

            if (A[first] > A[second]):
                # Uses Swap function
                swap(A, first, second)

# Function to find the highest number in the list.
def maxIt(numbers):
    maxNum = numbers[0]
    for i in numbers:
        if i > maxNum:
            maxNum = i
    return maxNum

# Start main
def main():

    # Creates the numbers array.
    numbers = []

    # Starts the loop to enter numbers into the array.
    done = False
    while not done:
        numInput = getNum("Please enter an integer or < 0 to finish >: ")

        # Stores every input from numInput into numbers.
        numbers.append(numInput)

        #  Test condition to break out of loop '0'.
        if numInput is 0:

            # Prints the resulting max number once finished.
            print("The maximum value is: " + str(maxIt(numbers)))

            # Flag to stop the program once finished.
            done = True

main()

未通过 getNum 测试时的当前输出(str 或 float):

Please enter an integer or < 0 to finish >: 222
Please enter an integer or < 0 to finish >: 333
Please enter an integer or < 0 to finish >: 444
Please enter an integer or < 0 to finish >: 555
Please enter an integer or < 0 to finish >: 666
Please enter an integer or < 0 to finish >: 777
Please enter an integer or < 0 to finish >: 888
Please enter an integer or < 0 to finish >: 999
Please enter an integer or < 0 to finish >: 0
The maximum value is: 999

在 getNum/numInput 中输入 str 或 float 时出错:

Please enter an integer or < 0 to finish >: 222
Please enter an integer or < 0 to finish >: 333
Please enter an integer or < 0 to finish >: 444
Please enter an integer or < 0 to finish >: test
I was expecting an integer number, please try again...

Please enter an integer or < 0 to finish >: 555
Please enter an integer or < 0 to finish >: 666
Please enter an integer or < 0 to finish >: 0
Traceback (most recent call last):
  File "C:\Users\Bar\Desktop\IS115\Peretz_A9.py", line 64, in <module>
    main()
  File "C:\Users\Bar\Desktop\IS115\Peretz_A9.py", line 59, in main
    print("The maximum value is: " + str(maxIt(numbers)))
  File "C:\Users\Bar\Desktop\IS115\Peretz_A9.py", line 37, in maxIt
    if i > maxNum:
TypeError: '>' not supported between instances of 'NoneType' and 'int'

Answer 1

好吧，问题是当数字无效时，您的函数 getNum 返回 None，请尝试以下快速修复:

if numInput is not None:
    numbers.append(numInput)

但我也建议您阅读:

Why is "except: pass" a bad programming practice?

并尽量避免代码中出现空的 except 子句!