If PR author is the same as the committer, only mention them once. (GH-19)

Closes python/miss-islington#18

Author: Mariatta

backport/backport_pr.py

@@ -27,9 +27,15 @@ async def backport_pr(event, gh, *args, **kwargs):
                         if label['name'].startswith("needs backport to")]
 
         if branches:
-            message = "🐍🍒⛏🤖 " \
-                      f"Thanks @{created_by} for the PR, and @{merged_by} for merging it 🌮🎉." \
-                      f"I'm working now to backport this PR to: {', '.join(branches)}."
+            thanks_to = ""
+            if created_by == merged_by:
+                thanks_to = f"Thanks @{created_by} for the PR 🌮🎉."
+            else:
+                thanks_to = f"Thanks @{created_by} for the PR, and @{merged_by} for merging it 🌮🎉."
+            message = f"""\
+            {thanks_to}. I'm working now to backport this PR to: {', '.join(branches)}.
+            🐍🍒⛏🤖 
+            """
             util.comment_on_pr(issue_number, message)
 
             for branch in branches:

backport/tasks.py

@@ -37,11 +37,11 @@ def backport_task(commit_hash, branch, *, issue_number, created_by, merged_by):
         cp.backport()
     except cherry_picker.BranchCheckoutException:
         util.comment_on_pr(issue_number,
-                            f"""Sorry @{created_by} and @{merged_by}, I had trouble checking out the `{branch}` backport branch.
+                            f"""Sorry {util.get_participants(created_by, merged_by)}, I had trouble checking out the `{branch}` backport branch.
                             Please backport using [cherry_picker](https://pypi.org/project/cherry-picker/) on command line.""")
         cp.abort_cherry_pick()
     except cherry_picker.CherryPickException:
         util.comment_on_pr(issue_number,
-                            f"""Sorry, @{created_by} and @{merged_by}, I could not cleanly backport this to `{branch}` due to a conflict. 
+                            f"""Sorry, {util.get_participants(created_by, merged_by)}, I could not cleanly backport this to `{branch}` due to a conflict. 
                             Please backport using [cherry_picker](https://pypi.org/project/cherry-picker/) on command line.""")
         cp.abort_cherry_pick()

backport/util.py

@@ -37,3 +37,12 @@ def is_cpython_repo():
     except subprocess.SubprocessError:
         return False
     return True
+
+
+def get_participants(created_by, merged_by):
+    participants = ""
+    if created_by == merged_by:
+        participants = f"@{created_by}"
+    else:
+        participants = f"@{created_by} and @{merged_by}"
+    return participants