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[Python-Dev] Python startup time

Nick Coghlan ncoghlan at gmail.com
Thu Jul 20 22:52:11 EDT 2017 
On 21 July 2017 at 12:44, Nick Coghlan <ncoghlan at gmail.com> wrote:
> We can separately measure the cost of unmarshalling the code object:
>
> $ python3 -m perf timeit -s "import typing; from marshal import loads; from
> importlib.util import cache_from_source; cache =
> cache_from_source(typing.__file__); data = open(cache, 'rb').read()[12:]"
> "loads(data)"
> .....................
> Mean +- std dev: 286 us +- 4 us

Slight adjustment here, as the cost of locating the cached bytecode
and reading it from disk should really be accounted for in each
iteration:

$ python3 -m perf timeit -s "import typing; from marshal import loads;
from importlib.util import cache_from_source" "cache =
cache_from_source(typing.__spec__.origin); data = open(cache,
'rb').read()[12:]; loads(data)"
.....................
Mean +- std dev: 337 us +- 8 us

That will have a bigger impact when loading from spinning disk or a
network drive, but it's fairly negligible when loading from a local
SSD or an already primed filesystem cache.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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