Make pyimport able to return module attributes

[hoodmane]

Before this PR, pyimport can be used like: pyimport("package") or pyimport("package.module") but pyimport("package.attribute") fails. This updates pyimport to also work to get package attributes.

• Add a CHANGELOG entry
• Add / update tests
• Add new / update outdated documentation

[hoodmane]

@ryanking13 another possibility is to add an optional second fromlist argument:

pyodide.pyimport(path, fromlist);

So that you could do:

const { PyodideConsole, repr_shorten, BANNER } = pyodide.pyimport(
  "pyodide.console",
  ["PyodideConsole", "repr_shorten", "BANNER"]
);

[hoodmane]

I guess I'll add that here and we can discuss.

[ryanking13]

Thanks @hoodmane!

For me, pyimport("package.attribute") seems slightly weird as it is not a supported behavior in Python. For instance,

import sys.platform

will raise exception: No module named 'sys.platform'; 'sys' is not a package.

So I am +1 for adding fromlist argument (or probably with some other name).

[hoodmane]

pyimport("package.attribute") seems slightly weird as it is not a supported behavior in Python.

Well we are already deviating from import a.b since if you do __import__("pkg.module") it returns pkg whereas we are returning pkg.module. So we behave more like from pkg import module than import pkg.module already. I think supporting pyimport("pkg.attribute") as well meaning from pkg import attribute actually makes the mental model more consistent. It's also convenient. WDYT?

It is a little bit weird having:

pyimport("pkg.module")            ==> from pkg import module
pyimport("pkg.module", fromlist)  ==> from pkg.module import <fromlist>

but I don't think it's completely crazy.

Also, when we pass a fromlist do you think we should return an Array or an Object?

[ryanking13]

Well we are already deviating from import a.b since if you do import("pkg.module") it returns pkg whereas we are returning pkg.module.

I see. That makes sense. Then I think pyimport("package.attribute") seems fine to me.

About the fromlist parameter, I just realized that we can already do a similar thing in JavaScript using destructuring assignment syntax. For instance, things like:

const { PyodideConsole, repr_shorten, BANNER } = pyodide.pyimport("pyodide.console")
const { platform, version, path } = pyodide.pyimport("sys")

already works without any modification. So maybe we don't need the fromlist parameter so much?

[hoodmane]

we can already do a similar thing in JavaScript using destructuring assignment syntax.

Oh this is a great observation! The only very minor concern is that you create and leak a temporary PyProxy this way, but I think it shouldn't matter:

1. packages are already globally stored in sys.modules
2. you won't be creating a reference loop so this will eventually get cleaned out by the JS GC
3. this is happening in run-once setup code not in loops or anything.

So I will remove the fromlist but keep the attribute change.

[ryanking13]

Thanks!