类型错误：+ 不支持的操作数类型：“int”和“NoneType”

Question

I am new user in Python, I have a problem with the None type, I looked different question, but the problem persists.

my code is calculate factorial

def fact(k): 
    if k > 0: 
        result = k + fact(k-1) 
        print(result) 
    else: 
        result=0 
    return result

fact(3)

Answer 1

I tried your code and could not produce that error. I think you have some indentation issues where your loop is not following the logic you are expecting. Remember what is in the loop and what is out of the loop is dependent on the white space, so be careful with tabs and spaces.

Also there are some errors in your logic

1. you need k * fact(k-1) not +
2. the else should be result = 1

edited code is this:

def fact(k): 
    if k > 0: 
        result = k * fact(k-1) 
        print(result) 
    else: 
        result=1 
    return result

Also a more Pythonic way to write your function is to have it return the actual result instead of passing the result to a variable and returning the variable. My assumption is that you're printing the result within the function to trouble shoot as this certainly in your final version would be removed. Regardless, try this code instead:

def fact_v2(k): 
    if k > 0: 
        return k * fact_v2(k-1) 
    else: 
        return 1 

and you would call you function like this:

print(fact_v2(11))

Good luck, Python is a fun language and may seem intimidating at fist, but you'll get there!