avoid potential circular ref by lazy import

[akrherz]

Description Of Changes

Future proof code to allow metpy.calc.basic to import functions in metpy.calc.tools without a potential circular import.

Checklist

• Closes metpy.calc.tools imports metpy.calc.basic which creates potential circular import #1211
• Fully documented

[akrherz]

I suppose this could be considered an API break since this will fail after this PR:

from metpy.calc.tools import height_to_pressure_std

shrug.

[lgtm-com]

This pull request fixes 15 alerts when merging 5ea3cd0 into 8c1ca0a - view on LGTM.com

fixed alerts:

• 15 for Module-level cyclic import

[zbruick]

Do you mean from tools or from basic? If we can still do from metpy.calc.basic import height_to_pressure_std, then the intended API doesn't break, which I think we should still be able to do.

[akrherz]

Do you mean from tools or from basic?

From tools, since tools is currently doing this global import and thus exposing the basic function there. Do I get bonus points for resolving 15 LGTM issues, lol.

[zbruick]

Yeah we'll add it to our running list of brownie points. I'll shrug with you on this "API break". If users were importing it this way, they shouldn't have been.

[dopplershift]

I only consider metpy.calc to be the public API. Submodules in there are subject to rearranging at any time without warning. That’s why we go to the effort we do to put things in the metpy.calc namespace. All the docs, examples, and tests only use metpy.calc. If you see something that’s not, we need to fix it.

[dopplershift]

@akrherz What prompted you to see this? All the complaints from LGTM?

[akrherz]

@akrherz What prompted you to see this? All the complaints from LGTM?

My first paragraph in #1211 was what I was up to. I was attempting to add a dimensionality helper (#1209) in tools.py and realized the circular import possibility. I had not looked at LGTM.

[dopplershift]

UGH. I hadn't even seen that issue. Thanks for fixing!