> The reason to use $$(some-command) instead of the built-in function $(shell some-command) is that the expression will be evaluated every time it is called. [.

> The reason to use $$(some-command) instead of the built-in function $(shell some-command) is that the expression will be evaluated every time it is called. [...] When using $(shell ...) the expression gets evaluated only once and reused across all the recipes. I don't think the last sentence is true. As long as you define py using = and not := it will be evaluated every time it's used.