How to return two values from a function, that are created in the function? - Python

Question

def FindingTwoPrimes(n, p1, p2):
    p1 = 0
    p2 = 0
    n = 0
    primeList = []
    for num in range(1,101):
        if all(num%i!=0 for i in range(2,num)):
            primeList.append(num)
    print (primeList)
    print ("Length of Primelist = ", len(primeList))
    lengthOfPrimelist = len(primeList)
    p1 = primeList[random.randint(0,lengthOfPrimelist)]
    p2 = primeList[random.randint(0,lengthOfPrimelist)]
    n = p1 * p2
    print ("p1 =", p1)
    print ("p2 =", p2)
    return n
    return p1
    return p2


FindingTwoPrimes(n, p1, p2)
print(p1, p2, n)

So above is a function that will find two primes that I will use in the method of the public key encryption system. However, when I run the function it returns p1, p2 and n back as 0. Why is this and how do I solve it? Also, any methods to make this code more efficient would be appreciated :-)

Use return (n, p1, p2) and then get them as: n, p1, p2 = FindingTwoPrimes(n, p1, p2) — Ankur Ankan
– Ankur Ankan, Commented Oct 28, 2017 at 17:04

kvorobiev · Accepted Answer · 2017-10-28 17:24:08Z

Your function will return single value, because it execution will be finished after first return statement. You could return multiply values using a tuple

def FindingTwoPrimes(n, p1, p2):
...
    return n, p1, p2


n, p1, p2 = FindingTwoPrimes(n, p1, p2)
print(p1, p2, n)

Also, your code wouldn't work at all. In the beginning of function you assign zero values to all it args.

def FindingTwoPrimes(n, p1, p2):
    p1 = 0
    p2 = 0
    n = 0

Try to use variables with different names inside function.
As I understand, you trying to pass results back from function in arguments. This is bad idea. Use tuple to get results from function

def FindingTwoPrimes():
    p1 = 0
    p2 = 0
    n = 0
    ...
    return n, p1, p2

n, p1, p2 = FindingTwoPrimes()
print(p1, p2, n)

About last part of your question - how to make it more efficient. If you planning to call this function many times you could move primeList calculation outside of function.

def FindingTwoPrimes(primeList):
    lengthOfPrimelist = len(primeList)
    p1 = primeList[random.randint(0,lengthOfPrimelist)]
    p2 = primeList[random.randint(0,lengthOfPrimelist)]
    n = p1 * p2
    print ("p1 =", p1)
    print ("p2 =", p2)
    return n, p1, p2

primeList = [num for num in range(1,101) if all(num%i!=0 for i in range(2,num))]

print (primeList)
print ("Length of Primelist = ", len(primeList))

n, p1, p2 = FindingTwoPrimes(primeList)
print(p1, p2, n)

Sandeep Lade · Accepted Answer · 2017-10-28 17:42:28Z

1

There should be only one return in a function but you have 3. Change the below lines from

return n
return p1
return p2

to

return [n,p1,p2]

then change print statement as

print FindingTwoPrimes(n, p1, p2)

Also code in your function is wrong. Please change that as well

import random
def FindingTwoPrimes(n, p1, p2):
    primeList = []
    for num in range(1,101):
        if all(num%i!=0 for i in range(2,num)):
            primeList.append(num)
    lengthOfPrimelist = len(primeList)
    p1 = primeList[random.randint(0,lengthOfPrimelist)]
    p2 = primeList[random.randint(0,lengthOfPrimelist)]
    n = p1 * p2
    return [p1,p2,n]

print FindingTwoPrimes(10, 11, 12)

edited Oct 28, 2017 at 17:42

answered Oct 28, 2017 at 17:05

Sandeep Lade

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2 Comments

kvorobiev Over a year ago

Why do you pass arguments to a function, if they are not used inside it?

Sandeep Lade Over a year ago

Could be OP wants to do some more things inside function with first value n. That's why i didn't remove.

Francisco Gonzalez · Accepted Answer · 2017-10-28 17:06:43Z

-1

for solve this only need

(n, p1, p2) = FindingTwoPrimes(n, p1, p2)

answered Oct 28, 2017 at 17:06

Francisco Gonzalez

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1 Comment

Stefan Pochmann Over a year ago

That's not the only change needed.

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