Python: How do I use a function's returned value in later code?

Question

I've just started learning Python and am trying to do an exercise.

I feel like I am missing something really basic as I can't get some values that are returned to affect my code.

The point of the following code is to print the prime factors of a user input fraction, except that it will only print the entered fraction's prime factors and not the simplified fractions.

def gcd(a,b):
    while b:
        a,b = b,a%b
    return a
def simplify_fraction(numerator,denominator):
    cd = gcd(numerator,denominator)
    (simple_num,simple_denom) = (numerator/cd,denominator/cd)
    if simple_denom == 1:
        return simple_num
    elif cd == 1:
        return simple_num,simple_denom
    else:
        return simple_num,simple_denom
def prime_factors(n):
    i = 2
    factors = []
    while i * i <= n:
        if n % i:
            i += 1
        else:
            n //= i
            factors.append(i)
    if n > 1:
        factors.append(n)
    return factors
while True:
    try:
        while True:
            fraction = input("Input a positive fraction then press enter:")
            numerator,denominator = fraction.split("/")
            numerator = int(numerator)
            denominator = int(denominator)
            if denominator == 0:
                raise ValueError
            elif numerator < 0:
                print("That is not a positive fraction, please try again.")
                continue
            elif denominator < 0:
                print("That is not a positive fraction, please try again.")
                continue            
            elif numerator == 0:
                print(str(numerator) + " / " + str(denominator) + " -> [0]")
            elif numerator == 1:
                print(str(fraction) + " -> [1] / " + str(prime_factors(denominator)))
            elif int(denominator) == 1:
                print(str(fraction) + " -> " + str(prime_factors(numerator)))
            else:
                simplify_fraction(numerator,denominator)

I'm sure I'm missing something here to link my simplify_fraction function to my this code block but I can't figure out what that is.

                print(str(fraction) + " -> " + str(prime_factors(numerator)) + " / " + str(prime_factors(denominator))) 
            while True:
                character = str(input('Continue (y/n)? '))
                if character == "y":
                    break
                if character == "n":
                    quit()
                else:
                    print ("That was not a valid choice, please select (y/n).")
                    continue
except ValueError:
    print("That is not a fraction, please try again.")
    continue

Here's 2 examples:

An input of 3/9 gives 3/9 -> [3] / [3,3]. I want it to be 3/9 -> [1] / [3].

An input of 138/24 gives 138/24 - > [2,3,23] / [2,2,2,3]. I want it to be 138/24 -> [23]/[2,2]

Can someone please give me some advice on this?

I don't fully understand your code, but note that simplify_fraction(numerator,denominator) towards the end of your loop does nothing because you don't assign the result to anything. Just calling the function won't modify the strings in-place. — Kevin
– Kevin, Commented Apr 24, 2015 at 13:01
wow that's a lot of code as for question "how do I use function's return value". Try to shrink the unrelated code. — TarasB
– TarasB, Commented Apr 24, 2015 at 13:02
Hey Taras, sorry I know it is, I was trying to give the full picture to allow for complete understanding and clarity. And Kevin, yes that's the core of the problem... I am trying to figure out how to assign those results to modify the strings in place... working on a string variation at the moment, hoping it works. — Aaron M
– Aaron M, Commented Apr 24, 2015 at 13:15

Aaron M · Accepted Answer · 2015-04-24 14:45:26Z

Tried a few more ways to achieve this over past couple hours and got it sorted. Felt I had answer this as it's now moot so... Here's the finished code:

def gcd(a,b):
    while b:
        a,b = b,a%b
    return a
def simplify_fraction(numerator,denominator):
    cd = gcd(numerator,denominator)
    (simple_num,simple_denom) = (numerator/cd,denominator/cd)
    return int(simple_num),int(simple_denom)
def prime_factors(n):
    i = 2
    factors = []
    while i * i <= n:
        if n % i:
            i += 1
        else:
            n //= i
            factors.append(i)
    if n > 1:
        factors.append(n)
    return factors
while True:
    try:
        while True:
            fraction = input("Input a positive fraction then press enter:")
            numerator,denominator = fraction.split("/")
            numerator = int(numerator)
            denominator = int(denominator)
            if denominator == 0:
                raise ValueError
            elif numerator < 0:
                print("That is not a positive fraction, please try again.")
                continue
            elif denominator < 0:
                print("That is not a positive fraction, please try again.")
                continue
            simple_num,simple_denom = simplify_fraction(numerator,denominator)
            if simple_denom == 1 and simple_num == 0:
                print(str(fraction) + " -> [0]")
            elif simple_denom == 1:
                print(str(fraction) + " -> " + str(prime_factors(simple_num)))
            elif simple_num == 1:
                print(str(fraction) + " -> [1] / " + str(prime_factors(simple_denom)))
            else:
                print(str(fraction) + " -> " + str(prime_factors(simple_num)) + " / " + str(prime_factors(simple_denom)))
            while True:
                character = str(input('Continue (y/n)? '))
                if character == "y":
                    break
                if character == "n":
                    quit()
                else:
                    print ("That was not a valid choice, please select (y/n).")
                    continue
except ValueError:
    print("That is not a valid fraction, please try again.")
    continue

Here's a test of the program:

Input a positive fraction then press enter: -6/2
That is not a positive fraction, please try again.
Input a positive fraction then press enter: 6/-2
That is not a positive fraction, please try again.
Input a positive fraction then press enter: 10/0
That is not a valid fraction, please try again.
Input a positive fraction then press enter: 0/0
That is not a valid fraction, please try again.
Input a positive fraction then press enter: 0/10
0/10 -> [0]
Continue (y/n)? y
Input a positive fraction then press enter: 138/24
138/24 -> [23] / [2,2]
Continue (y/n)? y
Input a positive fraction then press enter: 24/138
24/138 -> [2,2] / [23]
Continue (y/n)? u
That was not a valid choice, please select (y/n).
Continue (y/n)? tt
That was not a valid choice, please select (y/n).
Continue (y/n)? Y
That was not a valid choice, please select (y/n).
Continue (y/n)? y
Input a positive fraction then press enter: 66
That is not a valid fraction, please try again.
Input a positive fraction then press enter: 1024/512
1024/512 -> [2]
Continue (y/n)? y
Input a positive fraction then press enter: 1024/511
1024/511 = [2, 2, 2, 2, 2, 2, 2, 2, 2, 2] / [7, 73]
Continue (y/n)? n

Program exits.

My main mistake was in not setting the variables simple_num and simple_denom in my main code block.... knew it was something basic. Once that was done it was just a matter of tweaking to get it perfect.

WOW, what a rant. Sorry about that.

If anyone looks at this and knows of a better way to do it I'd love to see it... always trying to improve.

Thanks to this awesome website and community!

Collectives™ on Stack Overflow

Python: How do I use a function's returned value in later code?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related