Infra: Make check-peps’ _validate_post_history crash less (python#3511)

Co-authored-by: Pradyun Gedam <[email protected]>

Author: flying-sheep

check-peps.py

@@ -414,12 +414,15 @@ def _validate_post_history(line_num: int, body: str) -> MessageIterator:
 
     for offset, line in enumerate(body.removesuffix(",").split("\n"), start=line_num):
         for post in line.removesuffix(",").strip().split(", "):
-            if not post.startswith("`") and not post.endswith(">`__"):
+            prefix, postfix = (post.startswith("`"), post.endswith(">`__"))
+            if not prefix and not postfix:
                 yield from _date(offset, post, "Post-History")
-            else:
+            elif prefix and postfix:
                 post_date, post_url = post[1:-4].split(" <")
                 yield from _date(offset, post_date, "Post-History")
                 yield from _thread(offset, post_url, "Post-History")
+            else:
+                yield offset, f"post line must be a date or both start with “`” and end with “>`__”"
 
 
 def _validate_resolution(line_num: int, line: str) -> MessageIterator: