NUMBER=100000

class A(object):
    pass

a = A()
b = dict()

def test1():
    for x in xrange(NUMBER):
        if a.__class__ is A:
            pass
        if b.__class__ is A:
            pass

def test2():
    for x in xrange(NUMBER):
        if isinstance(a, A):
            pass
        if isinstance(b, A):
            pass

"""
timeit.py 'import shad; shad.test1()'
10 loops, best of 3: 61.9 msec per loop
timeit.py 'import shad; shad.test2()'
10 loops, best of 3: 102 msec per loop
"""