# 10 examples of 'python program to find prime number' in Python

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``20def prime(num):21    # num is actually a string because input() returns strings. We'll convert it to int22    num = int(num)2324    if num &lt; 0:25        print("Negative integers can not be prime")26        quit()27    if num is 1:28        print("1 is neither prime nor composite")29        # See how I lazily terminated program otherwise it'd forward "None"(default behaviour of python when function30        # returns nothing) rather than True or False. Which could mess up the program.31        # If we hit this if statement above statement is printed then program exits.32        quit()  # Now you don't need to get sys.exit() to exit python has quit to handle the same thing33    if num in [2, 3]:34        # if given argument is 2 or 3, it is prime. We used list without defining a variable which is perfectly valid35        return True36    if num % 2 == 0:  # excluding all even numbers except two.37        return False38    else:39        # Here we are starting counter variable from 3 in range. Second argument excludes numbers above one third40        # of the given argument. Third argument in range sets steps to take to 2. This makes loop to iterate odds41        for x in range(3, int(num/3), 2):42            # Checking if argument is divisible by counter. % is modulus operator which returns remainder of division43            if num % x == 0:44                return False45    # It's okay to have more than one return statement when program hits return statement it exits the function.46    return True``
``12def primes():13    yield 214    yield 31516    for i in itertools.count(start=5, step=2):17        if is_prime(i):18            yield i``
``7def isPrime(num):8    # Returns True if num is a prime number, otherwise False.910    # Note: Generally, isPrime() is slower than primeSieve().1112    # all numbers less than 2 are not prime13    if num &lt; 2:14        return False1516    # see if num is divisible by any number up to the square root of num17    for i in range(2, int(math.sqrt(num)) + 1):18        if num % i == 0:19            return False20    return True``
``23def findprimes(start, end):24	for i in range(start, end):25		if i not in Checked:26			Checked.append(i)27			if is_prime(i):28				Primes.append(i)``
``6def is_prime(n):7   '''8   checks if a number is prime9   '''10   if n &lt; 2:11      return False12   if n == 2:13      return True14   for x in range(2, int(n**0.5)+1, 2):15      if n % x == 0:16         return False17   return True``
``3def is_prime(n):4    i = 35    while i * i &lt;= n:6        if n % i == 0: return False7        i += 28    return True``
``1def is_prime(n):2	if n &lt; 2:3		return False45	i = 267	while i * i &lt;= n:8		if n % i == 0:9			return False1011		i += 11213	return True``
``6def countPrimes(self, n):7    notPrimes = []8    for k in range(n + 1):9        notPrimes.append(False)10    count = 011    for i in range(2, n):12        if notPrimes[i]:13            continue14        count += 115        for j in range(i * i, n, i):16            notPrimes[j] = True17    return count``
``21def is_prime(n):22    for i in xrange(2, int(sqrt(n)) + 1):23        if n % i == 0:24            return False2526    return True``
``3def is_prime(n):4    if n &lt;= 1:5        return False6    elif n == 2:7        return True8    elif n % 2 == 0:9        return False10    for i in xrange(3, int(sqrt(n))+1, 2):11        if n % i == 0:12            return False13    return True``