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This simple isprime(number) function checks if the given integer number is a prime number and returns True or False. The function makes sure that the number is a positive integer, and that 1 is not considered a prime number.
# prime numbers are only divisible by unity and themselves # (1 is not considered a prime number by convention) 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 squareroot 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 # test ... print isprime(1) # False print isprime(2) # True print isprime(3) # True print isprime(29) # True print isprime(345) # False print isprime(999979) # True print isprime(999981) # False # extra test ... print isprime(49) # False print isprime(95) # False