replace pkg_resources with importlib.metadata #953
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Importing pkg_resources has a side-effect of scanning every installed distribution on sys.path to load the metadata, especially the entry points defined in the packages. This can have a significant launch-time cost for command line applications when there are a lot of distributions to scan. Since cmd2 is only using pkg_resources to find the version of the installed package, pkg_resources can be replaced with importlib.metadata. The implementation in the new library is significantly faster because it goes immediately to the metadata file for the requested distribution, instead of scanning all of them. There are also no import-time side-effects. importlib.metadata is a new standard library module starting with python 3.8. For earlier versions, a compatible library has been released to PyPI as 'importlib_metadata'. This change adds the new dependency with a qualifier so that it is only applied to older versions of python, and then updates the places that were importing pkg_resources to look for the different versions of the new library instead. The documentation configuration is changed to import cmd2 itself to get its version, since the package has to be installed for the metadata to be available anyway. Signed-off-by: Doug Hellmann <doug@doughellmann.com>
Codecov Report
@@ Coverage Diff @@
## master #953 +/- ##
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- Coverage 97.72% 97.70% -0.03%
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Files 19 19
Lines 4177 4183 +6
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+ Hits 4082 4087 +5
- Misses 95 96 +1
Continue to review full report at Codecov.
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tleonhardt
approved these changes
Jul 12, 2020
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@dhellmann Hey Doug, thanks a ton for this fix! I had noticed that on some systems cmd2 had an abnormally large start time, but I had not had the time to get to the bottom of why.
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Thanks for the quick review, @tleonhardt ! |
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Importing pkg_resources has a side-effect of scanning every installed
distribution on sys.path to load the metadata, especially the entry
points defined in the packages. This can have a significant
launch-time cost for command line applications when there are a lot of
distributions to scan.
Since cmd2 is only using pkg_resources to find the version of the
installed package, pkg_resources can be replaced with
importlib.metadata. The implementation in the new library is
significantly faster because it goes immediately to the metadata file
for the requested distribution, instead of scanning all of them. There
are also no import-time side-effects.
importlib.metadata is a new standard library module starting with
python 3.8. For earlier versions, a compatible library has been
released to PyPI as 'importlib_metadata'. This change adds the new
dependency with a qualifier so that it is only applied to older
versions of python, and then updates the places that were importing
pkg_resources to look for the different versions of the new library
instead. The documentation configuration is changed to import cmd2
itself to get its version, since the package has to be installed for
the metadata to be available anyway.