Re: Naming scheme for Python packages

[Andreas Enge <andreas@enge.fr>]

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On Thu, Sep 05, 2013 at 03:00:27PM +0200, Ludovic Courtès wrote:
> BTW, I haven’t check whether this is the case already, but we need
> something like
>   (define (package-with-explicit-python p python)
>     ;; Return a version of P built for PYTHON.
>     (package (inherit p) ...))
> so we can just write:
>   (define python2-pytz
>     (package-with-explicit-python python-pytz python-2))

The attached patch does almost this, following our offline discussion on
how to create packages recursively on the fly:
- It adds an argument pair "#:python ,python-2", or replaces an already
  present argument "#:python something-else", and this recursively
  for all inputs and native-inputs that use the python build system.
- It rewrites the corresponding names from "python-..." to "python2-...",
  or adds a prefix "python2-".
So one can write
(define python2-pytz
  (package-with-explicit-python python-pytz))
As the second argument would always be python-2, I decided to drop it.

When trying this with python2-babel, the previous code in python.scm
(commented out in the attached patch) and the new one create almost the same
derivations, that differ only in
  /nix/store/4rrnwqsj8c086zzviyypr4fikb7pz49v-python2-babel-0.9.6-guile-builder
vs.
  /nix/store/5prbhg600qa9k8p0bgjs12p4dm682gn8-python2-babel-0.9.6-guile-builder
so that the final hash is also different.

Comments are welcome.

Andreas


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diff --git a/gnu/packages/python.scm b/gnu/packages/python.scm
index ce89281..aa2d15c 100644
--- a/gnu/packages/python.scm
+++ b/gnu/packages/python.scm
@@ -28,6 +28,7 @@
   #:use-module (gnu packages patchelf)
   #:use-module (guix packages)
   #:use-module (guix download)
+  #:use-module (guix utils)
   #:use-module (guix build-system gnu)
   #:use-module (guix build-system python)
   #:use-module (guix build-system trivial))
@@ -215,9 +216,7 @@ using Python 2.4 or higher and provides access to the Olson timezone database.")
     (license x11)))
 
 (define-public python2-pytz
-  (package (inherit python-pytz)
-    (name "python2-pytz")
-    (arguments (append (package-arguments python-pytz) `(#:python ,python-2)))))
+  (package-with-python2 python-pytz))
 
 (define-public python-babel
   (package
@@ -233,7 +232,8 @@ using Python 2.4 or higher and provides access to the Olson timezone database.")
         "03vmr54jq5vf3qw6kpdv7cdk7x7i2jhzyf1mawv2gk8zrxg0hfja"))))
     (build-system python-build-system)
     (inputs
-     `(("python-pytz" ,python-pytz)))
+     `(("python-pytz" ,python-pytz)
+       ("openssl" ,openssl)))
     (arguments `(#:tests? #f)) ; no test target
     (home-page "http://babel.edgewall.org/")
     (synopsis
@@ -246,9 +246,12 @@ access to various locale display names, localized number and date formatting,
 etc. ")
     (license bsd-3)))
 
+;; (define-public python2-babel
+;;   (package (inherit python-babel)
+;;     (name "python2-babel")
+;;     (inputs
+;;      `(("python2-pytz" ,python2-pytz)))
+;;     (arguments (append (package-arguments python-babel) `(#:python ,python-2)))))
+
 (define-public python2-babel
-  (package (inherit python-babel)
-    (name "python2-babel")
-    (inputs
-     `(("python2-pytz" ,python2-pytz)))
-    (arguments (append (package-arguments python-babel) `(#:python ,python-2)))))
+  (package-with-python2 python-babel))
diff --git a/guix/build-system/python.scm b/guix/build-system/python.scm
index 7ac93b2..a704d35 100644
--- a/guix/build-system/python.scm
+++ b/guix/build-system/python.scm
@@ -41,6 +41,56 @@
   (let ((python (resolve-interface '(gnu packages python))))
     (module-ref python 'python-wrapper)))
 
+(define (default-python2)
+  "Return the default Python 2 package."
+  (let ((python (resolve-interface '(gnu packages python))))
+    (module-ref python 'python-2)))
+
+(define-public (package-with-python2 p)
+  "Create a package with the same fields as P, which is assumed to use
+PYTHON-BUILD-SYSTEM and to be compiled with the default python, such that
+it is compiled with python 2 instead.  The name of P is prefixed with
+\"python2-\"; a potential existing prefix \"python-\" is dropped."
+  (let ((rewrite (lambda (x)
+                   ;; procedure taking a two-element list ("name" package)
+                   ;; and returning a two element list
+                   ;; ("name" (package-with-python2 package))
+                   (let ((name (car x))
+                         (content (car (cdr x))))
+                     (list name
+                           (if (package? content)
+                               (package-with-python2 content)
+                               content)))))
+        (build-system (package-build-system p)))
+    (package (inherit p)
+      (name
+        (let ((name (package-name p)))
+          (if (eq? build-system python-build-system)
+            (string-append "python2-"
+                           (if (string-prefix? "python-" name)
+                               (substring name 7)
+                               name))
+            name)))
+      (arguments
+        (let ((arguments (package-arguments p))
+              (python2 (default-python2)))
+          (if (eq? build-system python-build-system)
+            (if (member #:python arguments)
+                (substitute-keyword-arguments arguments ((#:python p) python2))
+                (append arguments `(#:python ,python2)))
+            arguments)))
+      (inputs
+        (let ((inputs (package-inputs p)))
+          (if (null? inputs)
+              '()
+              (map rewrite inputs))))
+      (native-inputs
+        (let ((native-inputs (package-native-inputs p)))
+          (if (null? native-inputs)
+              '()
+              (map rewrite native-inputs)))))))
+
+
 (define* (python-build store name source inputs
                        #:key
                        (python (default-python))