Hi,
> Is this a bug?
No it's not, the following snippet should work better.
--8<---------------cut here---------------start------------->8---
(fold-packages
(lambda (package lst)
(if (string-prefix? "python" (package-name package))
(cons (and=> (package-source package)
(lambda (source)
(origin-uri source)))
lst)
lst))
'())
--8<---------------cut here---------------end--------------->8---
Mathieu
