Sure, here is a Python function that checks if a number is prime and then uses this function to print all prime numbers from 1 to 100.

def is_prime(n):
    if n <= 1:
        return False
    elif n <= 3:
        return True
    elif n % 2 == 0 or n % 3 == 0:
        return False
    i = 5
    while i * i <= n:
        if n % i == 0 or n % (i + 2) == 0:
            return False
        i += 6
    return True

for num in range(1, 101):
    if is_prime(num):
        print(num)

In the is_prime function, we first handle the special cases of numbers less than or equal to 1 (which are not prime) and numbers less than or equal to 3 (which are prime). Then we check if the number is divisible by 2 or 3, in which case it is not prime. If it passes these checks, we then check divisibility for all numbers up to the square root of the number (since a larger factor of the number would be a multiple of some smaller factor that has already been checked). If the number is not divisible by any of these, it is prime.

Then we use this function in a loop from 1 to 100 to print all prime numbers in this range.