issue with for loop in Python

Question

I am trying to learn python and I have tried to convert a code snippet in js to python. I have created a function in js to calculate GCD as follows:

// program to find the GCD of two integers
let gcd
function GCD() {
// take input
const number1 = prompt('Enter a first positive integer: ')
const number2 = prompt('Enter a second positive integer: ')
// looping from 1 to number1 and number2
for (let i = 1; i <= number1 && i <= number2; i++) {
 if( number1 % i == 0 && number2 % i == 0) {
 gcd = i
 }
}
// display the gcd
document.write(`GCD of ${number1} and ${number2} is ${gcd}.`)
}
GCD()

If I supply the first integer as 9 and the second integer of 3, I get the GCD as 3.

I have tried to convert this to a python program as follows:

def gcd():
 gcd = 0
 num1 = int(input("Enter a first positive integer: "))
 num2 = int(input("Enter a second positive integer: "))
 
 for i in range(1, i<=num1 and i<=num2):
 if num1 % i == 0 and num2 % i == 0:
 gcd = i
 print(f"GCD of: {num1} and: {num2} is {gcd}")
gcd()

But I don't know how to get the for loop in python quite right. If I change the for statement to:

def gcd():
 gcd = 0
 num1 = int(input("Enter a first positive integer: "))
 num2 = int(input("Enter a second positive integer: "))
 for i in range(1, num1 and num2):
 if num1 % i == 0 and num2 % i == 0:
 gcd = i
 print(f"GCD of: {num1} and: {num2} is {gcd}")
gcd()

and I give the same input as before of 9 and 3, I get GCD of 1

• khelwood: for i in range(1, min(num1, num2)+1):
• user2371684: Thanks, that worked out :) but could you please explain the syntax? is the min I guess to set the min range and the +1 to set it to the correct amount of iterations, for example to get 6 iterations I set range to for I in range(1, 7):

Answer 1

You can't have an equivalent syntax as i <= number1 && i <= number2 as it is a boolean expression that works as stop condition which is checked at every iteration.

While a for loop in python code generates values with boudaries, to do the same, iterate until the lowest value:

for i in range(1, min(num1, num2) + 1):
 if num1 % i == 0 and num2 % i == 0:
 gcd = i

---

To use the condition of the JS code, you need a while loop:

i = 1
while i <= num1 and i <= num2:
 if num1 % i == 0 and num2 % i == 0:
 gcd = i
 i += 1

• user2371684: Thanks.. I need to understand the structure of a for loop in python :)

Answer 2

this is a solution based on while loop

def gcd():
 gcd=0
 num1 = int(input("Enter a first positive integer: "))
 num2 = int(input("Enter a second positive integer: "))
 i = 1
 while(i <= num1 and i <= num2):
 if(num1 % i == 0 and num2 % i == 0):
 gcd = i
 i = i + 1
 print("GCD : ", gcd)
gcd()