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Bizarre additional calling overhead.

>>def test_func():
.... pass
>>import new
test_func2 = new.function(test_func.func_code, {}, "test_func2")
<function test_func2 at 0x01B8C2F0>
<function test_func at 0x01B8C270>
>>import timeit
tf = timeit.Timer("test_func()", "from __main__ import test_func")
[0.2183461704377247, 0.18068215314489791, 0.17978585841498085]
>>tf2 = timeit.Timer("test_func2()", "from __main__ import test_func2")
[0.40015390239890891, 0.35893452879396648, 0.36034628133737456]
Why almost twice the calling overhead for a dynamic function?
Nov 2 '07 #1
2 1096
On Nov 2, 3:08 pm, "Chris Mellon" <arka...@gmail.comwrote:
>def test_func():

... pass
...>>import new
>test_func2 = new.function(test_func.func_code, {}, "test_func2")

<function test_func2 at 0x01B8C2F0>>>test_func

<function test_func at 0x01B8C270>>>import timeit
>tf = timeit.Timer("test_func()", "from __main__ import test_func")

[0.2183461704377247, 0.18068215314489791, 0.17978585841498085]>>tf2 = timeit.Timer("test_func2()", "from __main__ import test_func2")

[0.40015390239890891, 0.35893452879396648, 0.36034628133737456]

Why almost twice the calling overhead for a dynamic function?
So, I don't have an official explanation for why it takes twice as
long, but the only difference between the two functions I could find
was that test_func.func_globals was set to globals() and
test_func2.func_globals was an empty dict. When I re-created
test_func2 with globals set to globals() it ran just as fast as
>>test_func2 = new.function(test_func.func_code, globals(), "test_func")
tf2 = timeit.Timer("test_func2()", "from __main__ import test_func2")
[0.18119118491313202, 0.18396220748718406, 0.18722407456812107]
[0.18125124841299112, 0.17981251807145782, 0.18517996002287873]


Nov 3 '07 #2
On Fri, 02 Nov 2007 17:08:06 -0500, Chris Mellon wrote:
>>>def test_func():
... pass
>>>import new
test_func2 = new.function(test_func.func_code, {}, "test_func2")
[snip results of timeit]
Why almost twice the calling overhead for a dynamic function?
When I time the functions, I get a lot of variability. The minimum value
is probably the best one to look at:
.... "from __main__ import test_func").repeat(20))
.... "from __main__ import test_func2").repeat(20))
Disassembling the code does not give any hints:
>>import dis
2 0 LOAD_CONST 0 (None)
2 0 LOAD_CONST 0 (None)

Which is what we should expect, because both functions have the same code:
>>test_func.func_code is test_func2.func_code
But try this:
>>test_func3 = new.function(test_func.func_code,
.... globals(), 'test_func3')
.... "from __main__ import test_func3").repeat(20))
Hmmm... it looks like the difference in speed has to do with the globals,
not the fact that it is created dynamically. I wonder why?

Nov 3 '07 #3

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