bpo-40807: Show warnings once from codeop._maybe_compile (#20486)

* bpo-40807: Show warnings once from codeop._maybe_compile

* Move catch_warnings

* news

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

1 files changed, 13 insertions, 9 deletions

diff --git a/Lib/codeop.py b/Lib/codeop.py
index 835e68c09b..7e192ea6a1 100644
--- a/Lib/codeop.py
+++ b/Lib/codeop.py
@@ -57,6 +57,7 @@ Compile():
 """
 
 import __future__
+import warnings
 
 _features = [getattr(__future__, fname)
              for fname in __future__.all_feature_names]
@@ -83,15 +84,18 @@ def _maybe_compile(compiler, source, filename, symbol):
     except SyntaxError:
         pass
 
-    try:
-        code1 = compiler(source + "\n", filename, symbol)
-    except SyntaxError as e:
-        err1 = e
-
-    try:
-        code2 = compiler(source + "\n\n", filename, symbol)
-    except SyntaxError as e:
-        err2 = e
+    # Suppress warnings after the first compile to avoid duplication.
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore")
+        try:
+            code1 = compiler(source + "\n", filename, symbol)
+        except SyntaxError as e:
+            err1 = e
+
+        try:
+            code2 = compiler(source + "\n\n", filename, symbol)
+        except SyntaxError as e:
+            err2 = e
 
     try:
         if code: