PyCharm IDE cannot find references to unit classes

[jamesbraza]

• unyt version: 2.7.1
• Python version: 3.6.9
• Operating System: macOS Mojave v10.14.3
• PyCharm version: 2019.2.6 CE

Description

Since unit instances are added to unyt's namespace at runtime, PyCharm (Python IDE) cannot introspect the attributes of a given unit. PyCharm declares "Cannot find reference".

I would like to be able to use PyCharm's introspection to aid in developer speed (code completion) and decrease the chances of attribute errors.

Possible solution: this question suggests making a stub file. I am not sure if this is feasible.

What I Did

See this question on Stack Overflow.

from unyt import degC

t1 = 0 * degC
t1.convert_to_base()

[ngoldbaum]

I wonder if we dynamically created an __all__ attribute at import time, would PyCharm be able to resolve the references then? I don't have PyCharm installed so can't really help much with debugging this one.

If PyCharm is doing this purely using text analysis then I don't think there's much we can do. We're definitely not going to go to explicitly listing everything since that would be a maintainance nightmare.

[JBorrow]

This is also a problem in Visual Studio Code, IIRC.

[jamesbraza]

@JBorrow what do you do? Just ignore it? Do you ever use code completion with unit instances?

@ngoldbaum I installed unyt and inserted __all__ = ["degC"] into unyt.__init__.py.

The result is my base Python file now no longer complains "Cannot find reference", it now knows that degC comes from unyt. However, it still doesn't know that degC is a Unit instance. PyCharm just suggests that it's an object. It does not suggest the method .copy or the property .units while typing.

[ngoldbaum]

Another idea that might work is to generate __init__.py at build time (e.g. orchestrated by setup.py) and replace the globals manipulation with code literals.

[JBorrow]

@JDusub83

I in general just ignore this, yes. Usually I am working inside a function with type hints:

The red underline is telling me that Mpc is not found in unyt.

[jamesbraza]

Back to the __all__ approach. Adding a global variable type annotation on the units right after __all__ solves the problem... PyCharm can now infer the type!

Inside unyt.__init__.py:

__all__ = ["degC"]
degC: Unit

I am unsure which is better. Does anyone have any thoughts?

• Adding each unit to an __all__ attribute and specifying a global variable type annotation
• Replacing globals manipulation with code literals

[ngoldbaum]

Is it possible to dynamically define type annotations? If so, does PyCharm recognize those? It's also not clear to me from your examples that PyCharm would know how to deal with a dynamically defined __all__.