函数内部while循环触发ValueError的问题分析及修复（add_up函数）

Let's break down why your code is throwing a ValueError when inputting "Stop" first, then fix it up properly.

The Root Problem #

Your current code tries to convert every input directly to an integer with string = int(input()) before checking if it's "Stop". When the user types "Stop", Python can't turn that string into an integer—hence the ValueError crash.

Revised Code with Error Handling #

Here's a robust version that handles the "Stop" case gracefully, plus deals with other invalid non-integer inputs:

def add_up():
    total = 0
    while True:
        # Grab the raw input first, trim any accidental whitespace
        user_input = input().strip()
        
        # Check if we need to stop first
        if user_input == "Stop":
            break
        
        # Try converting to integer, catch errors if input is invalid
        try:
            number = int(user_input)
            total += number
        except ValueError:
            # Optional: Let the user know their input was invalid
            print(f"Oops, '{user_input}' isn't a valid integer. Please enter a number or 'Stop'.")
    
    print(f"Total sum: {total}")

add_up()

Key Improvements: #

• Check for "Stop" first: We get the raw string input before attempting any conversion, so we can exit the loop immediately when the user types "Stop".
• Try-except block: This catches ValueError whenever the input can't be converted to an integer (like random text or symbols), preventing the program from crashing.
• Cleaner loop structure: Using while True with a break statement makes the exit condition clearer than your original loop setup.
• Whitespace handling: strip() ensures accidental spaces around "Stop" (like " Stop ") still trigger the exit.

Quick Note on Your Original Code's Quirks #

• Initializing string = 0 (an integer) and then checking string is not "Stop" is a bit odd—integers and strings will never be the same object, so that condition was always True anyway. The bigger issue was the premature integer conversion, though.

内容的提问来源于stack exchange，提问作者Liviu Iosif