Re: Import package and generate use-module

[Ekaitz Zarraga]

Hi,

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Saturday, April 24, 2021 11:26 AM, phodina via <help-guix@gnu.org> wrote:

> I'm making a package for octoprint which is imported from PyPI. guix import 
> -r octoprint generates the template to build the package.
>
> However, I'm missing the :#use-module ... in order to build the package when 
> I add (define-module (python-octoprint). Given the fact there are tens of 
> inputs doing it manually seems tedious and writing a script to parse the 
> package definition seems like reinventing the wheel as I'm certainly not the 
> first person to run into this issue.
>
> So is there a way to automate also this part?
>
> Let me give you context:If I look at Guix package repository 
> gnu/packages/python-xyz.scm I see there definitions of packages:
>
> (define-public python-numpy
> (package
> (name "python-numpy")
> ...
>
> If I have another package that depends on python-numpy I just provide the 
> name in e.g. inputs and I don't have to import it with #:use-module within 
> this file.
>
> However, when I run guix import pypi PKG I get package definition and when I 
> run guix build -f python-octoprint.scm I get this error:
>
> /tmp/python-octoprint.scm:275:6: In procedure propagated-inputs:
> error: python-flask: unbound variable
> hint: Did you forget `(use-modules (gnu packages python-web))'?
>
> Of course writing down all the unbound variables by hand is tedious and 
> error-prone. And since guix gives a hint is there a way to write the 
> dependency into the file?
>
> And the question in general is: When I find out that the program is not 
> packaged and I want to write the package definition and then verify it 
> installs and runs correctly, what steps should I take?
>
> guix pull pypi PKG > PKG.scm
>
> Add 'define-module'
>
> ====================
>
> ??
> guix build -f PKG.scm
>
> Note: Doesn't matter if it's python or rust program. I'm interested in the 
> workflow
>
> Kind regards
> Petr Hodina
>
> Sent with ProtonMail Secure Email.

I'm not sure if I understand it correctly.

What I understand is you need to add the define-module like in
any guile file, but you don't need to import every single
variable in the module you are importing. You just import the
whole module and every `define-public` from the module will
be available.

See for instance this:

https://gitlab.com/ekaitz-zarraga/guix-packages/-/blob/master/electronics.scm#L7

That import provides *all* the public variables from the `python`
module, not only one.

The case of `python-numpy` you describe works because variables
share module scope, so they don't need to import other vars in
the same file: they can already see them.

In your case you are pretty much fine importing a couple of
modules: python-web for flask, and probably python-science or
so.

The lazy approach is:
I try to `guix build` if there's a missing module add it with
#:use-modules, as shown in the example.
Rinse and repeat.

The direct approach is to use tools like `guix show` to check
the module where your inputs are described and import them.

For example:

```
$ guix show python-flask
 name: python-flask
version: 1.1.2
outputs: out
systems: x86_64-linux i686-linux
dependencies: python-click@7.1.2 [...]
location: gnu/packages/python-web.scm:2946:2
homepage: https://www.palletsprojects.com/p/flask/
license: Modified BSD
[...]
```

So now you know it is defined in `python-web`, as it says
in the `location` field. Now, you can add the `#:use-modules`
form that includes `python-web` to your module definition.

If other of your inputs is located in the same module you
*don't* need to import it again, because it will be already
known by that import.

So the point here to clarify is:
Use modules don't import PACKAGES, they import THE WHOLE
FILE, with all the (public) packages it contains. So it's
not as tedious as you suggested.[^1]

I hope this helps.

Best,
Ekaitz

[^1]: you can actually choose specific variables to import,
exclude some or use a prefix for the imported ones.
But our normal usage is just to import the whole file. See:
https://www.gnu.org/software/guile/manual/html_node/Creating-Guile-Modules.html
and:
https://www.gnu.org/software/guile/manual/html_node/Using-Guile-Modules.html