test_is_int.py

#!/usr/bin/env python

def is_int1(v):
    return v.lstrip('+-').isdigit()

def is_int2(v):
    try:
        int(v)
        return True
    except ValueError:
        return False

def is_int3(v):
    try:
        int(v)
        return True
    except:
        return False


def is_int4(v):
    try:
        return isinstance(int(v), int)
    except:
        pass
    return False


import timeit

if __name__ == '__main__':
    number = 1000000
    for s in ["238764", "2", "sdkjhf", "4398265.238476"]:
        for ver in range(4):
            func = 'is_int%d' % (ver+1,)
            print 'func=%s, input=%s, time=%f' % (func, s, timeit.timeit('%s("%s")' % (func, s), setup='from __main__ import %s' % (func,), number=number))

Running on my system, I get:

func=is_int1, input=238764, time=0.243841
func=is_int2, input=238764, time=0.416296
func=is_int3, input=238764, time=0.417030
func=is_int4, input=238764, time=0.530820
func=is_int1, input=2, time=0.240771
func=is_int2, input=2, time=0.411695
func=is_int3, input=2, time=0.409882
func=is_int4, input=2, time=0.522021
func=is_int1, input=sdkjhf, time=0.241361
func=is_int2, input=sdkjhf, time=2.180622
func=is_int3, input=sdkjhf, time=1.839075
func=is_int4, input=sdkjhf, time=1.903009
func=is_int1, input=4398265.238476, time=0.244732
func=is_int2, input=4398265.238476, time=2.249253
func=is_int3, input=4398265.238476, time=1.884120
func=is_int4, input=4398265.238476, time=2.002077