On 26 July 2014 05:03, Raoul Duke <[email protected]> wrote:
>> It works well in Python, and mostly well in .NET x32.
>
> ja wohl. but, what is the overhead? i'd love to be able to log like
crazy. :-)
>
> (ha ha "overhead" that's a joke in python oh boy i crack myself up.)
With CPython:
[wleslie@dirac:~/src/port-fairy]
17:24:47 $ cat frametest.py
import timeit
# control
print timeit.Timer(
"f()", """
import sys
def f():
result = []
frame = sys._getframe
for _ in xrange(4):
code = f.func_code
result.append((code.co_firstlineno, code.co_filename, code.co_name))
frame = 7
return result
""").timeit(100000)
print timeit.Timer(
"f()", """
import sys
def f():
result = []
frame = sys._getframe()
while frame is not None:
code = frame.f_code
result.append((frame.f_lineno, code.co_filename, code.co_name))
frame = frame.f_back
return result
""").timeit(100000)
[wleslie@dirac:~/src/port-fairy]
17:24:58 $ python frametest.py
0.167432069778
0.20387005806
For reference, result is this:
[(11, '<timeit-src>', 'f'), (17, '<timeit-src>', 'inner'), (195,
'/usr/lib/python2.7/timeit.py', 'timeit'), (15, 'frametest.py', '<module>')]
So I can access almost all of the information required for the traceback
about 500,000 times per second on my laptop, and perhaps 25% of that work
is walking the stack. Those convenient 'previous frame' references would
be a bit harder to determine if python didn't store that information on
every function call, so in a language made for performance you could
imagine f_back and f_code would be a little more expensive.
Turning the filename and line number into the text of a traceback (by
looking at the file, which is probably cached) is significantly slower it
seems, as traceback.extract_stack (from the traceback module) does.
I dare say I don't know what work goes into maintaining f_lineno. I
understand it can be synthesised from the program counter together with
code.co_firstlineno and code.co_lnotab.
Now one thing about python is that frame objects are mutable - you can use
them to set local variables and such. And because existing optimising
compilers don't do sufficient effect analysis - and there is no interface
for read-only frame access - they assume (last I checked) that if you're
grabbing the frame, you probably just want your program to go very, very
slow (;
--
William Leslie
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