Implement Pynac->Python callback for function::subs()

[vbraun]

This patch lets us optionally change the behavior of subs() on symbolic functions.

Depends on #15198

Component: symbolics

Author: Volker Braun

Branch/Commit: bdb03bc

Reviewer: Jean-Pierre Flori

Issue created by migration from https://trac.sagemath.org/ticket/14800

[vbraun]

Attachment: trac_14800_subs.patch.gz

Initial patch

[vbraun]

Description changed:

--- 
+++ 
@@ -1,3 +1,5 @@
 This patch lets us optionally change the behavior of `subs()` on symbolic functions.
 
+Depends on the Pynac enhancement https://bitbucket.org/pynac/pynac/pull-request/3/implement-function-subs-callback-into/diff
 
+Apply [attachment: trac_14800_subs.patch](https://github.com/sagemath/sage-prod/files/10658026/trac_14800_subs.patch.gz) to the Sage library

[eviatarbach]

Dependencies: #15198

[jpflori]

Description changed:

--- 
+++ 
@@ -1,5 +1 @@
 This patch lets us optionally change the behavior of `subs()` on symbolic functions.
-
-Depends on the Pynac enhancement https://bitbucket.org/pynac/pynac/pull-request/3/implement-function-subs-callback-into/diff
-
-Apply [attachment: trac_14800_subs.patch](https://github.com/sagemath/sage-prod/files/10658026/trac_14800_subs.patch.gz) to the Sage library

[jpflori]

comment:4

Works fine (with all dependencies installed of course).

Maybe the __repr__ method needs more love, as well as the doctests (or at least some indirect doctest tags).

---

New commits:

a6a0d6b	Implement Pynac->Python callback for function::subs().
5fe48d7	Fix typo.

[jpflori]

Branch: u/jpflori/ticket/14800

[jpflori]

Reviewer: Jean-Pierre Flori