[Python-Dev] Change PEP 399 import recommendation (original) (raw)

Stefan Krah stefan at bytereef.org
Sat Oct 12 19:39:49 CEST 2013

Stefan Behnel <stefan_ml at behnel.de> wrote:

FWIW, I think this definitely makes sense in cases where the C implementation is essentially a complete replacement of the original module, such as in this case. I even sometimes suggest compiling Python modules with Cython if the import time matters.

For "normal" accelerator modules that only replace a part of a Python module with a native implementation, this is less likely to make a large enough difference to make up for the additional complexity due to the code split.

I wonder how big the cumulative effect is (yes, I should really measure instead of wondering ;)).

Anyhow, to measure the effect for decimal in a real world application, these are the startup times of Python if decimal is imported at startup:

diff --git a/Lib/site.py b/Lib/site.py --- a/Lib/site.py +++ b/Lib/site.py @@ -72,6 +72,7 @@ import os import builtins import _sitebuiltins +import decimal

Prefixes for site-packages; add additional prefixes like /usr/local here

PREFIXES = [sys.prefix, sys.exec_prefix]

With the current scheme:

$ time ./python -c "pass"

real 0m0.040s user 0m0.036s sys 0m0.004s

With the patch for #19232:

$ time ./python -c "pass"

real 0m0.023s user 0m0.016s sys 0m0.004s

But I agree that decimal.py is a special case, since it's very large and imports many other modules.

Stefan Krah

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