Infra: Add extlinks for python/cpython issues and PRs (#4426)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Author: hugovk

peps/conf.py

@@ -83,7 +83,10 @@
 # This config is a dictionary of external sites,
 # mapping unique short aliases to a base URL and a prefix.
 # https://www.sphinx-doc.org/en/master/usage/extensions/extlinks.html
+_repo = "python/cpython"
 extlinks = {
+    "cpython-issue": (f"https://github.com/{_repo}/issues/%s", f"{_repo}#%s"),
+    "cpython-pr": (f"https://github.com/{_repo}/pull/%s", f"{_repo}#%s"),
     "pypi": ("https://pypi.org/project/%s/", "%s"),
 }
 

peps/pep-0749.rst

@@ -825,8 +825,7 @@ This allows the following implementation strategy:
 * The generated ``__annotate__`` function uses the set to determine
   which annotations were defined in the class or module body, and return only those.
 
-This was implemented in `python/cpython#130935
-<https://github.com/python/cpython/pull/130935>`__.
+This was implemented in :cpython-pr:`130935`.
 
 Specification
 -------------