为什么在输出中没有打印？？？ Python

Question

import json

file = 'favnum.json'

def save_fav():
    number = input('Type your favourite number: ')
    with open(file, 'w') as f:
        num = json.dump(number, f)
        return num

def get_stored_number():
    try:   
        with open(file) as f:
            number_fav = json.load(f)
        
    except FileNotFoundError:
        return None
    else:
        return number_fav

def main_number():
    num = get_stored_number()
    
    if num:
        print('your favourite number is: ')
        print(num)
    
    else:
        print('the number had not saved before\nthus you have to save it')
        numbers = save_fav()
        print('your number is saved')
        print(numbers)

main_number()

Output:

the number had not saved before
thus you have to save it
Type your favourite number: 3.14
your number is saved
None

Answer 1

您应该在函数 save_fav() 中返回 number 而不是 num

Answer 2

Because that json.dump does not return anything except None and you are saving it in num, and returning num so function returns num too. So return anything meaningful else like even an empty string.

Answer 3

I think your function:

def save_fav():
    number = input('Type your favourite number: ')
    with open(file, 'w') as f:
        num = json.dump(number, f)
        return num

should be this instead:

def save_fav():
    number = input('Type your favourite number: ')
    with open(file, 'w') as f:
        json.dump(number, f)
    return number

In your version, json.dump returns None , and so that's what you are returning from the function, and then printing later on.