Check if a number is a prime number (Python) - Page 2

n & 1 returns the last bit of number, which is 1 for odd numbers (True like, e.g. 7 = 0b111) and 0 for even (e.g. 4 = 0b100)

def isprime(x):
     for i in range(2,x):
        if x%i == 0:
           return False
        elif: x%i != 0 and i == x-1:
           return True

A simple timing example:

import time

def print_timing(func):
    """
    a decorator function to time another function
    time.clock() works on Windows systems only
    you can use time.time() instead, but it gets updated less
    frequently and can give 0.0 results on faster functions
    """
    def inner(*arg):
        """*arg are the arguments of function func"""
        t1 = time.clock()
        res = func(*arg)
        t2 = time.clock()
        # time is in milliseconds
        print('%s took %0.3f ms' % (func.__name__, (t2-t1)*1000.0))
        return res
    return inner

@print_timing
def isprime(x):
     for i in range(2, x):
        if x%i == 0:
           return False
        elif x%i != 0 and i == x-1:
           return True

@print_timing
def isprime5(n):
    if n == 2 or n == 3: return True
    if n < 2 or n%2 == 0: return False
    if n < 9: return True
    if n%3 == 0: return False
    sqr = int(n**0.5)
    f = 5
    while f <= sqr:
        if n%f == 0: return False
        if n%(f+2) == 0: return False
        # loop every 6th integer
        f += 6
    return True


isprime(13999979)  # isprime took 404.684 ms

isprime5(13999979) # isprime5 took 0.022 ms

isprime5(135999979) # isprime5 took 0.610 ms

isprime(135999979)  # MemoryError

def isprime(x):
    if x%2 != 0:
       for i in range(3,x,2):
          if x%i == 0:
             return False
          elif x%i != 0 and i == x-2:
              return True
#A much faster way of processing the code#

def isprime(x):
    if x%2 != 0:
       for i in range(3,x,2):
          if x%i == 0:
             return False
          elif x%i != 0 and i == x-2:
              return True
    elif x == 0 or x == 1 or x == 2:
            return False
    else:
        return False

correction of above, more efficient

for num in range(3,40):  #put the range of numbers
    isp = 0
    for j in range(2,num//2+1):
        if(num%j==0):
             isp = 1
             break
    if(isp!=1):
        print(num)

def is_prime(k):
    for u in range(2, (k // 2) + 1):
        if k % u == 0:
            return False
    return True