[Python-Dev] Change PEP 399 import recommendation

[Stefan Krah]

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