Closes #14267: Corrected computation of rollover filename.

Lib/logging/handlers.py

@@ -270,9 +270,10 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
                         dstAtRollover = time.localtime(newRolloverAt)[-1]
                         if dstNow != dstAtRollover:
                             if not dstNow:  # DST kicks in before next rollover, so we need to deduct an hour
-                                newRolloverAt = newRolloverAt - 3600
+                                addend = -3600
                             else:           # DST bows out before next rollover, so we need to add an hour
-                                newRolloverAt = newRolloverAt + 3600
+                                addend = 3600
+                            newRolloverAt += addend
                     result = newRolloverAt
         return result
 
@@ -323,11 +324,20 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
             self.stream.close()
             self.stream = None
         # get the time that this sequence started at and make it a TimeTuple
+        currentTime = int(time.time())
+        dstNow = time.localtime(currentTime)[-1]
         t = self.rolloverAt - self.interval
         if self.utc:
             timeTuple = time.gmtime(t)
         else:
             timeTuple = time.localtime(t)
+            dstThen = timeTuple[-1]
+            if dstNow != dstThen:
+                if dstNow:
+                    addend = 3600
+                else:
+                    addend = -3600
+                timeTuple = time.localtime(t + addend)
         dfn = self.baseFilename + "." + time.strftime(self.suffix, timeTuple)
         if os.path.exists(dfn):
             os.remove(dfn)
@@ -337,19 +347,18 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
                 os.remove(s)
         self.mode = 'w'
         self.stream = self._open()
-        currentTime = int(time.time())
         newRolloverAt = self.computeRollover(currentTime)
         while newRolloverAt <= currentTime:
             newRolloverAt = newRolloverAt + self.interval
         #If DST changes and midnight or weekly rollover, adjust for this.
         if (self.when == 'MIDNIGHT' or self.when.startswith('W')) and not self.utc:
-            dstNow = time.localtime(currentTime)[-1]
             dstAtRollover = time.localtime(newRolloverAt)[-1]
             if dstNow != dstAtRollover:
                 if not dstNow:  # DST kicks in before next rollover, so we need to deduct an hour
-                    newRolloverAt = newRolloverAt - 3600
+                    addend = -3600
                 else:           # DST bows out before next rollover, so we need to add an hour
-                    newRolloverAt = newRolloverAt + 3600
+                    addend = 3600
+                newRolloverAt += addend
         self.rolloverAt = newRolloverAt
 
 class WatchedFileHandler(logging.FileHandler):