为什么我的循环继续无限循环？

Question

I have a bit of code and I'm having trouble understanding why the loop is an infinite loop even though I have an else condition which should end the loop.

def add1(*args):
    total = 0
    add = True

    for num in args:
        while add == True:
            if num!=6:
                total = total + num
            else:
                add = False
    return total

add1(1,2,3,6,1)

My question is, I have an else statement that changes the add to 'False' hence the loop should stop but for some reason it doesn't.

However, if I make a slight alteration to the code as such, it stops:

def add1(*args):
    total = 0
    add = True

    for num in args:
        while add == True:
            if num!=6:
                total = total + num
                break
            else:
                add = False
    return total

add1(1,2,3,6,1)

basically, adding a break. I don't understand how expert python coders actually interpret 'break' in their minds. I've read articles on break, but still can't seem to understand it quite as well. I don't understand why the 'break' is needed and why the 'else' can't suffice.

Answer 1

When you enter the for loop, num gets the value 1 (the first value in args ). Then you enter the while loop (since add is True). Now, because num does not equal 6 , you enter the if block, so the else block does NOT executes. Then, you just return to the while loop, and the value of num doesn't change. Then, because num does not equal 6 (remember it didn't change, it is still 1 ), once again you enter the if block, and so on until you terminate the program.

When you add the break , you exit the closest loop, which in this case is the while loop, so the for loop continues, until num gets the value 6 , and add becomes False . When that happens, the while loop never executes again.

Answer 2

def add1(*args):
    total = 0
    add = True

    for num in args:
        if add == True:
            if num!=6:
                total = total + num
            else:
                add = False
                break      #breaking the for loop for better performance only.
    return total

add1(1,2,3,6,1)

this adds till 6 is not encountered. you are using while loop unnecessarily. you have to break the infinite loop by some condition and that condition is when num!=6. even your else part can break the infinite while loop, but according to me the while loop itself is unnecessary.

Answer 3

I believe the purpose of your code is to sum up elements in *args up to first occurrence of number 6. If that is the case, the while loop is redundant here. Changing the first code snippet:

def add1(*args):
    total = 0

    for num in args:
        if num != 6:
            total = total + num
        else:
            break
    return total


add1(1, 2, 3, 6, 1)

---

What actually happens in your original code is that the num variable doesn't change in any way when iterating in while loop, so it never enters the else part, effectively getting stuck on the first input argument that is not 6, see below:

def add1(*args): # [1, 2, 3, 6, 1]
    total = 0
    add = True

    for num in args:  # first element is 1. num = 1
        while add == True:
            if num != 6:  # num = 1 always
                total = total + num
                # adding break here gets out of the while loop on first iteration, changing num = 2
                # and later to 3, 6...
            else:  # else is never reached
                add = False
    return total


add1(1, 2, 3, 6, 1)

Answer 4

You should change the below codes:

from

if num != 6:

to

if total != 6: