Allow adding arbitrary labels to metrics when generating output

prometheus_client/registry.py

@@ -82,6 +82,18 @@ def collect(self):
         for collector in collectors:
             yield from collector.collect()
 
+    def labelled_registry(self, extra_labels):
+        """Returns object that collects metrics with additional labels.
+
+        Returns an object which upon collect() will return
+        samples with additional labels given in the dictionary.
+
+        Intended usage is:
+            generate_latest(REGISTRY.labelled_registry(['a_timeseries']))
+
+        Experimental."""
+        return LabelledRegistry(extra_labels, self)
+
     def restricted_registry(self, names):
         """Returns object that only collects some metrics.
 
@@ -128,6 +140,19 @@ def get_sample_value(self, name, labels=None):
         return None
 
 
+class LabelledRegistry:
+    """Metric collector registry that applies extra labels to metrics."""
+
+    def __init__(self, extra_labels, registry):
+        self._extra_labels = extra_labels
+        self._registry = registry
+
+    def collect(self):
+        for metric in self._registry.collect():
+            metric.samples = [s._replace(labels={**s.labels, **self._extra_labels}) for s in metric.samples]
+            yield metric
+
+
 class RestrictedRegistry:
     def __init__(self, names, registry):
         self._name_set = set(names)

tests/test_core.py

@@ -929,6 +929,13 @@ def test_restricted_registry_does_not_yield_while_locked(self):
         for _ in registry.restricted_registry(['target_info', 's_sum']).collect():
             self.assertFalse(registry._lock.locked())
 
+    def test_labelled_registry(self):
+        extra_labels = {'label1': 'value1'}
+        registry = CollectorRegistry(extra_labels)
+        Counter('c_total', 'help', registry=registry)
+        metrics = list(registry.labelled_registry(extra_labels).collect())
+        self.assertEqual(metrics[0].samples[0].labels, extra_labels)
+
 
 if __name__ == '__main__':
     unittest.main()