Can you please help me in solving in this question in Python programing on composite numbers

prime_numbers = [2, 3, 5, 7, 11, 13, 17, 19, 23,
     29, 31, 37, 41, 43, 47, 53, 59,
     61, 67, 71, 73, 79, 83, 89, 97,
     101, 103, 107, 109, 113, 127,
     131, 137, 139, 149, 151, 157,
     163, 167, 173, 179, 181]

for i in prime_numbers:
    assert_true(isPrime(i), str(i) + ' is prime')

not_prime_numbers = [1, 8, 12, 18, 20, 27, 28, 30,
     42, 44, 45, 50, 52, 63, 66,
     68, 70, 75, 76, 78, 92, 98,
     99, 102, 138, 148, 150, 156, 158]

for i in not_prime_numbers:
    assert_true(not(isPrime(i)), str(i) + ' is not prime')

#test existence of docstring
assert_true(len(isPrime.__doc__) > 1, "there is no docstring for isPrime")
print("Success!")
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-28-29884f8bc4fb> in <module>
     11 
     12 for i in prime_numbers:
---> 13     assert_true(isPrime(i), str(i) + ' is prime')
     14 
     15 not_prime_numbers = [1, 8, 12, 18, 20, 27, 28, 30,

NameError: name 'assert_true' is not defined

def isPrime(x):
    """Returns whether or not the given number x is prime.

    A prime number is a natural number greater than 1 that cannot be formed
    by multiplying two smaller natural numbers.

    For example:
    - Calling isPrime(11) will return True
    - Calling isPrime(71) will return True
    - Calling isPrime(12) will return False
    - Calling isPrime(76) will return False
    """
    
    # your code here
   
    if num>1:
        s=int(num/2)
        for i in range(2,s+1):
            if num%i==0:
                return("not Prime")
                break
        return("Prime")
print(isPrime(239))