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I found that creation of a class is way slower than instantiation of a class. >>> from timeit import Timer as T >>> def calc(n): ... return T("class Haha(object): pass").timeit(n) <<After several these 'calc' things, at least one of them have a big number, eg. 100000>> >>> calc(9000) 15.947055101394653 >>> calc(9000) 17.39099097251892 >>> calc(9000) 18.824054956436157 >>> calc(9000) 20.33335590362549 Yeah, create 9000 classes took 16 secs, and becomes even slower in the subsequent calls. And this: >>> T("type('Haha', b, d)", "b = (object, ); d = {}").timeit(9000) gives similar results. But instantiation don't suffer: >>> T("Haha()", "class Haha(object): pass").timeit(5000000) 0.8786070346832275 5000000 instances in less than one sec. What makes the creation this expensive? And why the creation process become slower? EDIT: How to reproduce: start a fresh python process, the initial several "calc(10000)"s give a number of 0.5 on my machine. And try some bigger values, calc(100000), it can't end in even 10secs, interrupt it, and calc(10000), gives a 15sec. EDIT: Additional fact: If you gc.collect() after 'calc' becomes slow, you can get the 'normal' speed at beginning, but the timing will increasing in subsequent calls >>> from a import calc >>> calc(10000) 0.4673938751220703 >>> calc(10000) 0.4300072193145752 >>> calc(10000) 0.4270968437194824 >>> calc(10000) 0.42754602432250977 >>> calc(10000) 0.4344758987426758 >>> calc(100000) ^CTraceback (most recent call last): File "<stdin>", line 1, in <module> File "a.py", line 3, in calc return T("class Haha(object): pass").t

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