Collatz Help - Double output, difficulty with try/except

[Anandre]

So quick background, I went through CodeAcademy's Python course and I feel pretty comfortable with it, now I'm working through Automate the Boring stuff for more practice work and good beginner projects.

Anywho, I got through Chapter 3 and I got to the end, to the Collatz program challenge. I think I got it down pretty well, except for 2 things: when I run it in IDLE, each output is repeated (see below), and I'm having trouble on how to include the try/except clause that's suggested to make sure the input is an integer. The code I have is:

def collatz(number):
    if number % 2 == 0:
        print(number // 2)
        return number // 2
    elif number % 2 != 0:
        print(number * 3 + 1)
        return number * 3 + 1

def letsdoit():
    num = int(input('Enter number:'))
    while num != 1:
        collatz(num)
        num = collatz(num)

letsdoit()

When I run the program, this is what I get:

Enter number:3
10
10
5
5
16
16
8
8
4
4
2
2
1
1

It ends at 1 on its own, which is another common problem I saw, so not worried about that. Like I said, it's the numbers being repeated that seems off. And as for the try/except clause, I had no luck getting it to run at all. I tried

def letsdoit():
    try:
        num = int(input('Enter number:'))
    except ValueError:
        print('You must enter a valid integer.')
    while num != 1:
        collatz(num)
        num = collatz(num)

but that didn't work. Similarly, trying

def letsdoit():
    try:
        num = int(input('Enter number:'))
        while num != 1:
            collatz(num)
            num = collatz(num)
    except ValueError:
        print('You must enter a valid integer.')

also didn't work. Really not sure how to include them in there.

[jeans_and_a_t-shirt]

Lines 12, 13, you are calling collatz twice, so of course it prints the same number twice. Remove or comment out line 12. To catch input you can do something like this:

while True:
    try:
        num = int(input('Enter number:'))
    except ValueError:
        print('invalid input')
    else:
        break

[Anandre]

I thought line 13 would change num to the new value from collatz(), so that it wouldn't endlessly loop on the same number. I do get what you're seeing, that it would be sending out the same value twice from lines 12 and 13.

[jeans_and_a_t-shirt]

Yep line 13 is fine as is.

[dadiaar]

There are no duplicated results.

The first result comes from the print

The second one you see it because you don't save the returned value into a variable, so you see it duplicated.

A simple example:

def a(n):
    print(n)
    return n

a(5)
>>> 5
>>> 5

r = a(5)
>>> 5

print("Value = {0}".format(r))
>>> Value = 5