bpo-30522: Implemented a method to allow setting a logging.StreamHander's stream. (GH-2921)

2 files changed, 34 insertions, 0 deletions

diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py
index f9bfb79..54d4e88 100644
--- a/Lib/logging/__init__.py
+++ b/Lib/logging/__init__.py
@@ -997,6 +997,26 @@ class StreamHandler(Handler):
         except Exception:
             self.handleError(record)
 
+    def setStream(self, stream):
+        """
+        Sets the StreamHandler's stream to the specified value,
+        if it is different.
+
+        Returns the old stream, if the stream was changed, or None
+        if it wasn't.
+        """
+        if stream is self.stream:
+            result = None
+        else:
+            result = self.stream
+            self.acquire()
+            try:
+                self.flush()
+                self.stream = stream
+            finally:
+                self.release()
+        return result
+
     def __repr__(self):
         level = getLevelName(self.level)
         name = getattr(self.stream, 'name', '')
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 8884562..6d0b234 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -698,6 +698,20 @@ class StreamHandlerTest(BaseTest):
         finally:
             logging.raiseExceptions = old_raise
 
+    def test_stream_setting(self):
+        """
+        Test setting the handler's stream
+        """
+        h = logging.StreamHandler()
+        stream = io.StringIO()
+        old = h.setStream(stream)
+        self.assertIs(old, sys.stderr)
+        actual = h.setStream(old)
+        self.assertIs(actual, stream)
+        # test that setting to existing value returns None
+        actual = h.setStream(old)
+        self.assertIsNone(actual)
+
 # -- The following section could be moved into a server_helper.py module
 # -- if it proves to be of wider utility than just test_logging