Prime Number Check Acts Strange

Prime number check acts strange

You need to stop iterating once you know a number isn't prime. Add a break once you find prime to exit the while loop.

Making only minimal changes to your code to make it work:

a=2
num=13
while num > a :
  if num%a==0 & a!=num:
    print('not prime')
    break
  i += 1
else: # loop not exited via break
  print('prime')

Your algorithm is equivalent to:

for a in range(a, num):
    if a % num == 0:
        print('not prime')
        break
else: # loop not exited via break
    print('prime')

If you throw it into a function you can dispense with break and for-else:

def is_prime(n):
    for i in range(3, n):
        if n % i == 0:
            return False
    return True

Even if you are going to brute-force for prime like this you only need to iterate up to the square root of n. Also, you can skip testing the even numbers after two.

With these suggestions:

import math
def is_prime(n):
    if n % 2 == 0 and n > 2: 
        return False
    for i in range(3, int(math.sqrt(n)) + 1, 2):
        if n % i == 0:
            return False
    return True

Note that this code does not properly handle 0, 1, and negative numbers.

We make this simpler by using all with a generator expression to replace the for-loop.

import math
def is_prime(n):
    if n % 2 == 0 and n > 2: 
        return False
    return all(n % i for i in range(3, int(math.sqrt(n)) + 1, 2))

code that check if number is prime number

The range function creates an array of numbers between its parameters.
For example:

>>> range(1, 4)
=> [1, 2, 3]

In your code you're saying a%b which is finding the remainder between a number the user inputted and a range object. Think of the range object as a python list. So what you're doing is 5 % [1, 2, 3] that doesn't make sense. Check this separate thread to find out how to implement a prime number checker in python. Python Prime number checker

Determine Prime Number in Python DataFrame

I copy and pasted a function to find out if a number is prime from here:

Python Prime number checker

Then I use .apply() to apply this function to every value in column 'Trx':

def isprime(n):
    '''check if integer n is a prime'''

    # make sure n is a positive integer
    n = abs(int(n))

    # 0 and 1 are not primes
    if n < 2:
        return False

    # 2 is the only even prime number
    if n == 2: 
        return True    

    # all other even numbers are not primes
    if not n & 1: 
        return False

    # range starts with 3 and only needs to go up 
    # the square root of n for all odd numbers
    for x in range(3, int(n**0.5) + 1, 2):
        if n % x == 0:
            return False

    return True

df['Voucher'] = df['Trx'].apply(isprime)

Resulting dataframe:

    Name    Email                  Trx  Voucher
0   John    john.doe@gmail.com      30  False
1   Sarah   sarah@gmail.com          7  True
2   Bob bob@yahoo.com               11  True
3   Chad    chad@outlook.com        21  False
4   Karen   karen@outlook.com       20  False
5   Dmitri  dmitri@rocketmail.com   17  True

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