A comment about a build phase.

> [...]
> +         (replace 'check
> +           (lambda _
> +             (invoke "python" "-m" "pytest" "-v")
> +            #t)))))

This needs to be something like

+ (replace 'check
+   (lambda* (#:key tests? #:allow-other-keys)
+     (when tests?
+       (invoke "python" "-m" "pytest" "-v"))))

By respecting 'tests?', the --without-tests build transformation can be used.
(Try "guix build python-cooler --without-tests=python-cooler").
This can also be important for cross-compilation (dunno if it applies here
though).

Trailing #t are not required anymore. The warning that results if it is removed
will disappear once core-updates is merged.

Greetings,
Maxime.