The virtualenv mode is trying to be smart and checks whether it can
write to $out, which for some reason fails on darwin.
> virtualenv: error: argument dest: the destination . is not write-able at /nix/store
But what does work is creating it in the pwd and moving it to $out,
because mv just does what it is told.
Allow python3.tests to eval on other platforms than linux, by excluding
conda tests when not on linux, because they include alsa-lib, which is
linux-only.
Python package sets can be overridden by overriding an interpreter
and passing in `packageOverrides = self: super: {...};`. This is fine
in case you need a single interpreter, however, it does not help you
when you want to override all sets.
With this change it is possible to override all sets at once by
appending a list of "extensions" to `pythonPackagesExtensions`.
From reading the implementation you might wonder why a list is used, and
not
`lib.composeExtensions`? The reason is the latter requires knowledge of
the library function. This approach should be easier for most users
as it is similar to how we append to lists of e.g. inputs or patches
when overriding a derivation.
Thiago Kenji Okada