如何验证Python字典用户输入？里程表读数非数字时抛出异常

Hey there! Let's break down how to add proper input validation to your Python dictionary code so you can handle non-numeric inputs gracefully.

First, your current code uses int(input(...)) directly for odometer readings—this will throw a generic ValueError if someone enters text instead of a number, but it's not very user-friendly or explicit. Plus, your Model Year field is also a numeric value but isn't being validated at all! Here's how to fix that:

1. Create a Reusable Validation Function #

A dedicated function to handle numeric input checks will make your code cleaner and easier to maintain. You can choose to either prompt the user to try again, or throw a custom exception (whichever fits your use case).

Option 1: Prompt for Retry (User-Friendly)

This version keeps asking for input until a valid number is provided:

def get_valid_numeric_input(prompt):
    while True:
        user_input = input(prompt)
        try:
            return int(user_input)
        except ValueError:
            print(f"Oops! '{user_input}' isn't a valid number. Please try again.")

# Build your dictionary with validated inputs
Auto_details = {
    'Car brand': input('Car brand:'),
    'Car model': input('Car model:'),
    'Model Year': get_valid_numeric_input('Model Year:'),
    'Starting odometer reading': get_valid_numeric_input('Starting odometer reading:'),
    'Ending odometer reading': get_valid_numeric_input('Ending odometer reading:')
}

Option 2: Throw a Custom Exception (For Strict Validation)

If you want to explicitly raise a meaningful error instead of retrying, define a custom exception class for clearer error handling:

# Custom exception to make errors more descriptive
class InvalidNumericInputError(ValueError):
    """Raised when input is not a valid integer"""
    pass

def get_valid_numeric_input(prompt):
    user_input = input(prompt)
    try:
        return int(user_input)
    except ValueError:
        field_name = prompt.strip(':')
        raise InvalidNumericInputError(f"Invalid input for '{field_name}': '{user_input}' is not a valid integer.") from None

# Build the dictionary with validated inputs
Auto_details = {
    'Car brand': input('Car brand:'),
    'Car model': input('Car model:'),
    'Model Year': get_valid_numeric_input('Model Year:'),
    'Starting odometer reading': get_valid_numeric_input('Starting odometer reading:'),
    'Ending odometer reading': get_valid_numeric_input('Ending odometer reading:')
}

Bonus: Add Extra Validation Rules #

If you want to ensure odometer readings are positive (since you can't have negative miles!), you can extend the function:

def get_valid_numeric_input(prompt, allow_negative=False):
    while True:
        user_input = input(prompt)
        try:
            num = int(user_input)
            if not allow_negative and num < 0:
                print("Please enter a positive number.")
                continue
            return num
        except ValueError:
            print(f"Oops! '{user_input}' isn't a valid number. Please try again.")

Use it for odometer fields like this:

'Starting odometer reading': get_valid_numeric_input('Starting odometer reading:'),

Key Improvements #

• Reusability: The validation function works for all numeric fields, so you don't repeat code.
• Clarity: Either users get a helpful prompt to correct their input, or your code throws a custom exception that clearly describes what went wrong (no more vague default errors).
• Flexibility: You can easily add more rules (like positive numbers) without rewriting validation logic for every field.

内容的提问来源于stack exchange，提问作者Chinyama