find prime number - python code

[chang@sstest python]$ cat primeno.py
#!/usr/bin/python

def if_prime_no(number_n):
    yes_p = 1
    if number_n > 2:
        for i in range(2, number_n):
            if number_n%i==0:
                    #print (str(i) + " is not a prime number ")
                    yes_p=0

        if yes_p == 1:
            #print (str(number_n) + " is a prime number")
            return 1
        else:
            #print (str(number_n) + " is not a prime number")
            return 0

def all_prime(number_n):
    p = [2]
    for i in range(2, number_n+1):
        if if_prime_no(int(i))==1:
            p.append(i)
    return p

while True:
    your_number = raw_input ("Please enter the number or 'exit' to exit:")
    if your_number == 'exit':
        break
    else:
        if if_prime_no(int(your_number))==1:
            print (your_number + " is a prime number")
        else:
            print (your_number + " is not a prime number")

        print all_prime(int(your_number))



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[cng@sstest python]$ ./primeno.py
Please enter the number or 'exit' to exit:20
20 is not a prime number
[2, 3, 5, 7, 11, 13, 17, 19]
Please enter the number or 'exit' to exit:13
13 is a prime number
[2, 3, 5, 7, 11, 13]
Please enter the number or 'exit' to exit:exit