Support for 'extra' arguments

logging_prometheus/__init__.py

@@ -1,33 +0,0 @@
-import prometheus_client
-import logging
-
-
-log_entries = prometheus_client.Counter(
-    'python_logging_messages_total',
-    'Count of log entries by logger and level.',
-    ['logger', 'level'])
-
-
-class ExportingLogHandler(logging.Handler):
-    """A LogHandler that exports logging metrics for Prometheus.io."""
-    def emit(self, record):
-        log_entries.labels(record.name, record.levelname).inc()
-
-
-def export_stats_on_root_logger():
-    """Attaches an ExportingLogHandler to the root logger.
-
-    This should be sufficient to get metrics about all logging in a
-    Python application, unless a part of the application defines its
-    own logger and sets this logger's `propagate` attribute to
-    False. The `propagate` attribute is True by default, which means
-    that by default all loggers propagate all their logged messages to
-    the root logger.
-    """
-    logger = logging.getLogger()
-    logger.addHandler(ExportingLogHandler())
-
-
-# Just importing this module should make us export the metrics for the
-# root logger.
-export_stats_on_root_logger()

logging_prometheus/core.py

@@ -0,0 +1,39 @@
+import prometheus_client
+import logging
+
+
+class ExportingLogHandler(logging.Handler):
+    """A LogHandler that exports logging metrics for Prometheus.io."""
+    def __init__(self, level=logging.NOTSET, extra=None):
+        logging.Handler.__init__(self, level=level)
+
+        labels = ['logger', 'level']
+        self.extra = []
+        if extra:
+            if not isinstance(extra, list):
+                raise Exception("Argument 'extra' must be a list")
+            labels = labels + extra
+            self.extra = extra
+
+        self.log_entries = prometheus_client.Counter(
+            'python_logging_messages_total',
+            'Count of log entries by logger and level.',
+            labels)
+
+    def emit(self, record):
+        labels = [record.name, record.levelname] + [getattr(record, v, "unknown") for v in self.extra]
+        self.log_entries.labels(*labels).inc()
+
+
+def export_stats_on_root_logger(extra=None):
+    """Attaches an ExportingLogHandler to the root logger.
+
+    This should be sufficient to get metrics about all logging in a
+    Python application, unless a part of the application defines its
+    own logger and sets this logger's `propagate` attribute to
+    False. The `propagate` attribute is True by default, which means
+    that by default all loggers propagate all their logged messages to
+    the root logger.
+    """
+    logger = logging.getLogger()
+    logger.addHandler(ExportingLogHandler(extra=extra))

logging_prometheus/register.py

@@ -0,0 +1,5 @@
+from logging_prometheus.core import export_stats_on_root_logger
+
+# Just importing this module should make us export the metrics for the
+# root logger.
+export_stats_on_root_logger()

tests/test_logging.py

@@ -1,7 +1,7 @@
 import unittest
 import logging
 from prometheus_client import REGISTRY
-import logging_prometheus
+from logging_prometheus import register
 
 
 class TestLoggingPrometheus(unittest.TestCase):