Issue #4384: Added logging integration with warnings module using captureWarnings(). This change includes a NullHandler which does nothing; it will be of use to library developers who want to avoid the "No handlers could be found for logger XXX" message which can appear if the library user doesn't configure logging.

Lib/logging/__init__.py

@@ -46,8 +46,8 @@ except ImportError:
 
 __author__  = "Vinay Sajip <vinay_sajip@red-dove.com>"
 __status__  = "production"
-__version__ = "0.5.0.5"
-__date__    = "24 January 2008"
+__version__ = "0.5.0.6"
+__date__    = "03 December 2008"
 
 #---------------------------------------------------------------------------
 #   Miscellaneous module data
@@ -1488,3 +1488,58 @@ except ImportError: # for Python versions < 2.0
             old_exit(status)
 
     sys.exit = exithook
+
+# Null handler
+
+class NullHandler(Handler):
+    """
+    This handler does nothing. It's intended to be used to avoid the
+    "No handlers could be found for logger XXX" one-off warning. This is
+    important for library code, which may contain code to log events. If a user
+    of the library does not configure logging, the one-off warning might be
+    produced; to avoid this, the library developer simply needs to instantiate
+    a NullHandler and add it to the top-level logger of the library module or
+    package.
+    """
+    def emit(self, record):
+        pass
+
+# Warnings integration
+
+_warnings_showwarning = None
+
+def _showwarning(message, category, filename, lineno, file=None, line=None):
+    """
+    Implementation of showwarnings which redirects to logging, which will first
+    check to see if the file parameter is None. If a file is specified, it will
+    delegate to the original warnings implementation of showwarning. Otherwise,
+    it will call warnings.formatwarning and will log the resulting string to a
+    warnings logger named "py.warnings" with level logging.WARNING.
+    """
+    if file is not None:
+        if _warnings_showwarning is not None:
+            _warnings_showwarning(message, category, filename, lineno, file, line)
+    else:
+        import warnings
+        s = warnings.formatwarning(message, category, filename, lineno, line)
+        logger = getLogger("py.warnings")
+        if not logger.handlers:
+            logger.addHandler(NullHandler())
+        logger.warning("%s", s)
+
+def captureWarnings(capture):
+    """
+    If capture is true, redirect all warnings to the logging package.
+    If capture is False, ensure that warnings are not redirected to logging
+    but to their original destinations.
+    """
+    import warnings
+    global _warnings_showwarning
+    if capture:
+        if _warnings_showwarning is None:
+            _warnings_showwarning = warnings.showwarning
+            warnings.showwarning = _showwarning
+    else:
+        if _warnings_showwarning is not None:
+            warnings.showwarning = _warnings_showwarning
+            _warnings_showwarning = None