logging.py: CPython-compatible logging improvements.

This commit allows for logging handlers to be added to the root logger
and then used by non-root loggers that don't have their own handlers.

It also adds the (CPython-compatible) handlers argument
to logging.basicConfig() to ease this initialization:

    import logging
    sh = logging.StreamHandler()
    fh = logging.FileHandler("my.log", mode="a")
    logging.basicConfig(handlers=[sh, fh])

    root_logger = logging.getLogger() # uses sh and fh
    another_logger = logging.getLogger("another") # inherits handlers


It also adds the Logger.removeHandler() method and avoids repeated handler
addition.

It also adds the flush() method to StreamHandler and its subclasses.

It also correctly calls the superclass constructor from the StreamHandler
constructor and uses a default formatter if a Handler has none
set (as in PR #710).

Signed-off-by: Ned Konz <ned@productcreationstudio.com>

python-stdlib/logging/logging.py

@@ -25,6 +25,7 @@
 _stream = sys.stderr
 _default_fmt = "%(levelname)s:%(name)s:%(message)s"
 _default_datefmt = "%Y-%m-%d %H:%M:%S"
+_default_formatter = None
 
 
 class LogRecord:
@@ -43,25 +44,40 @@ def __init__(self, level=NOTSET):
         self.level = level
         self.formatter = None
 
+    @staticmethod
+    def _default_formatter():
+        global _default_formatter
+        if _default_formatter is None:
+            _default_formatter = Formatter()
+        return _default_formatter
+
     def close(self):
         pass
 
+    def flush(self):
+        pass
+
     def setLevel(self, level):
         self.level = level
 
     def setFormatter(self, formatter):
         self.formatter = formatter
 
     def format(self, record):
-        return self.formatter.format(record)
+        if self.formatter:
+            fmt = self.formatter
+        else:
+            fmt = self._default_formatter()
+        return fmt.format(record)
 
 
 class StreamHandler(Handler):
     def __init__(self, stream=None):
+        super().__init__()
         self.stream = _stream if stream is None else stream
         self.terminator = "\n"
 
-    def close(self):
+    def flush(self):
         if hasattr(self.stream, "flush"):
             self.stream.flush()
 
@@ -128,7 +144,7 @@ def log(self, level, msg, *args):
                 msg = msg % args
             self.record.set(self.name, level, msg)
             handlers = self.handlers
-            if not handlers:
+            if not self.hasHandlers():
                 handlers = getLogger().handlers
             for h in handlers:
                 h.emit(self.record)
@@ -161,7 +177,13 @@ def exception(self, msg, *args, exc_info=True):
             self.log(ERROR, buf.getvalue())
 
     def addHandler(self, handler):
-        self.handlers.append(handler)
+        if handler not in self.handlers:
+            self.handlers.append(handler)
+
+    def removeHandler(self, handler):
+        if handler in self.handlers:
+            handler.close()
+            self.handlers.remove(handler)
 
     def hasHandlers(self):
         return len(self.handlers) > 0
@@ -225,17 +247,28 @@ def basicConfig(
     stream=None,
     encoding="UTF-8",
     force=False,
+    handlers=None,
 ):
     if "root" not in _loggers:
         _loggers["root"] = Logger("root")
 
     logger = _loggers["root"]
 
-    if force or not logger.handlers:
+    if force:
         for h in logger.handlers:
             h.close()
         logger.handlers = []
 
+    if len([arg for arg in (filename, stream, handlers) if arg is not None]) > 1:
+        raise ValueError("can only set one of 'filename', 'stream' or 'handlers'")
+
+    if handlers is not None:
+        for h in handlers:
+            if h.formatter is None:
+                h.setFormatter(Formatter(format, datefmt))
+            logger.addHandler(h)
+
+    if not logger.hasHandlers():
         if filename is None:
             handler = StreamHandler(stream)
         else:
@@ -244,9 +277,10 @@ def basicConfig(
         handler.setLevel(level)
         handler.setFormatter(Formatter(format, datefmt))
 
-        logger.setLevel(level)
         logger.addHandler(handler)
 
+        logger.setLevel(level)
+
 
 if hasattr(sys, "atexit"):
     sys.atexit(shutdown)