import monty.json slowing down core import

[DanielYang59]

Summary

• from monty.json import xxx significantly slowly down core modules, as torch is eagerly imported
• Might need to look into other commonly used modules

For example:

python -X importtime -c "from pymatgen.core.structure import Structure" 2> pmg.log && tuna pmg.log

With torch installed (required by optional matgl):

After removing torch:

[janosh]

this is probably import overhead from loading pandas and maybe other big packages. if you start an interactive python session first, wait for it to load and then run poscar = Structure.from_file("./POSCAR") on its own, i expect it will be faster

[janosh]

have a look at #3563 which tried to reduce startup time by lazy-importing pandas only in code that actually needs it. that seems to have back-fired though based on this comment #3563 (comment). this takes more careful testing than i did in #3568 and materialsvirtuallab/monty#604 to make sure any changes really improve startup time

[DanielYang59]

This should also be partially fixed by materialsvirtuallab/monty#713, after that I would dig deeper and see what else is slowing down import