timeit of four isprime functions

''' timeit_isprime.py
check the speed of four isprime functions
'''

import timeit
import sys

print(sys.version)

def isprime2(n):
    '''
    check if integer n is a prime, return True or False
    '''
    # 2 is the only even prime
    if n == 2:
        return True
    # integers less than 2 and even numbers other than 2 are not prime
    elif n < 2 or not n & 1:
        return False
    #if n % 3 == 0: return False
    # loop looks at odd numbers 3, 5, 7, ... to sqrt(n)
    for i in range(3, int(n**0.5)+1, 2):
        if n % i == 0:
            return False
    return True

def isprime3(n):
    '''
    check if integer n is a prime, return True or False
    '''
    # 2 is the only even prime
    if n == 2:
        return True
    # integers less than 2 and even numbers other than 2 are not prime
    if n < 2:
        return False
    if not n & 1:  # even numbers
        return False
    # loop looks at odd numbers 3, 5, 7, ... to sqrt(n)
    for i in range(3, int(n**0.5)+1, 2):
        if n % i == 0:
            return False
    return True

def isprime4(n):
    '''
    check if integer n is a prime, return True or False
    uses a while loop, another way to write it, but is slower
    '''
    # 2 is the only even prime
    if n == 2:
        return True
    # integers less than 2 and even numbers other than 2 are not prime
    if n < 2:
        return False
    if n % 2 == 0:  # even numbers
        return False
    k = 3
    while k * k <= n:
         if n % k == 0:
             return False
         k += 2
    return True

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

# note 9999991 is a prime number
print(isprime2(9999991))
print(isprime3(9999991))
print(isprime4(9999991))
print(isprime5(9999991))

stmt = 'isprime2(9999991)'
find_function = 'from __main__ import isprime2'
t = timeit.Timer(stmt, setup=find_function)
# doing 1000 passes * 1000 gives the time in microseconds/pass
elapsed = (1000 * t.timeit(number=1000))
print("%s takes %0.3f micro-seconds/pass" % (stmt, elapsed))

stmt = 'isprime3(9999991)'
find_function = 'from __main__ import isprime3'
t = timeit.Timer(stmt, setup=find_function)
# doing 1000 passes * 1000 gives the time in microseconds/pass
elapsed = (1000 * t.timeit(number=1000))
print("%s takes %0.3f micro-seconds/pass" % (stmt, elapsed))

stmt = 'isprime4(9999991)'
find_function = 'from __main__ import isprime4'
t = timeit.Timer(stmt, setup=find_function)
# doing 1000 passes * 1000 gives the time in microseconds/pass
elapsed = (1000 * t.timeit(number=1000))
print("%s takes %0.3f micro-seconds/pass" % (stmt, elapsed))

stmt = 'isprime5(9999991)'
find_function = 'from __main__ import isprime5'
t = timeit.Timer(stmt, setup=find_function)
# doing 1000 passes * 1000 gives the time in microseconds/pass
elapsed = (1000 * t.timeit(number=1000))
print("%s takes %0.3f micro-seconds/pass" % (stmt, elapsed))


''' result ...
2.7.6 (default, Nov 10 2013, 19:24:18) [MSC v.1500 32 bit (Intel)]
True
True
True
True
isprime2(9999991) takes 197.503 micro-seconds/pass
isprime3(9999991) takes 196.715 micro-seconds/pass
isprime4(9999991) takes 361.188 micro-seconds/pass
isprime5(9999991) takes 168.592 micro-seconds/pass
'''