03/163: build/python: Add a new guix-pythonpath procedure.

[guix-commits]

apteryx pushed a commit to branch cu/farewell-to-pythonpath
in repository guix.

commit c3c5bdd2b0ea4588ecba424fdbf6df101d967d3d
Author: Maxim Cournoyer <maxim.cournoyer@gmail.com>
AuthorDate: Fri Jan 22 09:34:33 2021 -0500

    build/python: Add a new guix-pythonpath procedure.
    
    This procedure will be used in place where the static "PYTHONPATH" string 
used
    to be.
    
    * guix/build/python-build-system.scm (guix-pythonpath): New procedure.
---
 guix/build/python-build-system.scm | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/guix/build/python-build-system.scm 
b/guix/build/python-build-system.scm
index aad8625..77bd621 100644
--- a/guix/build/python-build-system.scm
+++ b/guix/build/python-build-system.scm
@@ -31,10 +31,12 @@
   #:use-module (ice-9 match)
   #:use-module (ice-9 ftw)
   #:use-module (ice-9 format)
+  #:use-module (ice-9 string-fun)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:export (%standard-phases
             add-installed-pythonpath
+            guix-pythonpath
             site-packages
             python-version
             python-build))
@@ -158,6 +160,13 @@
          (major+minor (take components 2)))
     (string-join major+minor ".")))
 
+(define (guix-pythonpath inputs)
+  "Derive the GUIX_PYTHONPATH_X_Y string , with the major and minor version
+numbers substituted for X and Y, respectively."
+  (let ((python (assoc-ref inputs "python")))
+    (string-append "GUIX_PYTHONPATH_"
+                   (string-replace-substring (python-version python) "." 
"_"))))
+
 (define (python-output outputs)
   "Return the path of the python output, if there is one, or fall-back to out."
   (or (assoc-ref outputs "python")