Starting from Python 3.10, the implementation of logging.FileHandler._open has
changed to use builtin open() unconditionally. Rather than continuing to
maintain a copy-pasted version of that method here, let's just remove it so it
can be inherited instead.

diff -ur ConcurrentLogHandler-0.9.1/src/cloghandler.py ConcurrentLogHandler-0.9.1.patched/src/cloghandler.py
--- ConcurrentLogHandler-0.9.1/src/cloghandler.py	2013-07-11 12:23:26.000000000 +1000
+++ ConcurrentLogHandler-0.9.1.patched/src/cloghandler.py	2021-08-01 18:40:45.341360592 +1000
@@ -152,21 +152,6 @@
         lock_file += ".lock"
         self.stream_lock = open(lock_file,"w")
     
-    def _open(self, mode=None):
-        """
-        Open the current base file with the (original) mode and encoding.
-        Return the resulting stream.
-        
-        Note:  Copied from stdlib.  Added option to override 'mode'
-        """
-        if mode is None:
-            mode = self.mode
-        if self.encoding is None:
-            stream = open(self.baseFilename, mode)
-        else:
-            stream = codecs.open(self.baseFilename, mode, self.encoding)
-        return stream
-    
     def _close(self):
         """ Close file stream.  Unlike close(), we don't tear anything down, we
         expect the log to be re-opened after rotation."""