CODEWITHSUNDEEP
python
Crimson Ninja
Crimson Ninja

Reputation: 13

How to understand the error in my Python program

code for printing factors of a number

I'm trying to code a program that prints the factors of a number, just as shown in the attached image, but the outcome is totally not what I'm expecting. (I just want the code to return factors of the specified number.) What am I doing wrong and what is the correct way of doing it?

Code:

number=42
factor_list=[]
for num in range(1,number+1):
    num=number/num
    if (number%num)==0:
        factor_list.append(num)
print(factor_list)

Output:

[42.0, 21.0, 14.0, 10.5, 7.0, 6.0, 5.25, 3.5, 3.0, 2.625, 2.0, 1.75, 1.5, 1.3125, 1.0]

Upvotes: 1

Views: 152

Answers (3)

Adon Bilivit
Adon Bilivit

Reputation: 26825

In Python, the division operator / will result in a float data type even if the values either side of it are int. For integer division you should use //

Having said that, what you need here is the modulo operator.

Here's a concise (but not necessarily most efficient) way of achieving your objective:

def factors(n):
    return [1] + [x for x in range(2, n + 1) if n % x == 0]

print(factors(4203))

Output:

[1, 3, 9, 467, 1401, 4203]

Fun fact:

If the length of the returned list from this function is 2 then n must be a prime number. Don't go using this function to test for primes though as it would be woefully inefficient

Upvotes: 0

matszwecja
matszwecja

Reputation: 7971

As to why your program does not work, let's see what is going on step by step:

    number=42
    factor_list=[]
    for num in range(1,number+1):      #for num in [1, 2, 3, 4, 5... 42] (Let's take 28 for example)
        num=number/num                 # num = 42 / 28; num = 1.5 now
        if (number%num)==0:            # 42 mod 1.5 == 0.0
            factor_list.append(num)    # so we add 1.5 to the list.
    print(factor_list)

See the problem in logic now?

Upvotes: 0

Roopa M
Roopa M

Reputation: 3009

Just remove the 4th line i.e num=number/num which produces quotients. you are trying to find modulus of number from those quotients that is the reason you are getting wrong answer. Here is the modified code which works.

number = 42
factor_list=[]
for num in range(1,number+1):
   if(number%num==0):
       factor_list.append(num)
print(factor_list)

Upvotes: 1

Related Questions