support prefix for prometheus exporter

CHANGELOG.md

@@ -32,6 +32,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4862](https://github.com/open-telemetry/opentelemetry-python/pull/4862))
 - `opentelemetry-exporter-otlp-proto-http`: fix retry logic and error handling for connection failures in trace, metric, and log exporters
   ([#4709](https://github.com/open-telemetry/opentelemetry-python/pull/4709))
+- `opentelemetry-exporter-prometheus`: Fix metric name prefix
+  ([#4895](https://github.com/open-telemetry/opentelemetry-python/pull/4895))
 
 ## Version 1.39.0/0.60b0 (2025-12-03)
 

docs/examples/metrics/prometheus-grafana/prometheus-monitor.py

@@ -11,7 +11,7 @@
 start_http_server(port=8000, addr="localhost")
 # Exporter to export metrics to Prometheus
 prefix = "MyAppPrefix"
-reader = PrometheusMetricReader(prefix)
+reader = PrometheusMetricReader(prefix=prefix)
 # Meter is responsible for creating and recording metrics
 set_meter_provider(MeterProvider(metric_readers=[reader]))
 meter = get_meter_provider().get_meter("view-name-change", "0.1.2")

exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py

@@ -38,7 +38,7 @@
 
     # Exporter to export metrics to Prometheus
     prefix = "MyAppPrefix"
-    reader = PrometheusMetricReader(prefix)
+    reader = PrometheusMetricReader(prefix=prefix)
 
     # Meter is responsible for creating and recording metrics
     set_meter_provider(MeterProvider(metric_readers=[reader]))
@@ -131,7 +131,7 @@ def _convert_buckets(
 class PrometheusMetricReader(MetricReader):
     """Prometheus metric exporter for OpenTelemetry."""
 
-    def __init__(self, disable_target_info: bool = False) -> None:
+    def __init__(self, disable_target_info: bool = False, prefix: str = "") -> None:
         super().__init__(
             preferred_temporality={
                 Counter: AggregationTemporality.CUMULATIVE,
@@ -142,9 +142,10 @@ def __init__(self, disable_target_info: bool = False) -> None:
                 ObservableGauge: AggregationTemporality.CUMULATIVE,
             }
         )
-        self._collector = _CustomCollector(disable_target_info)
+        self._collector = _CustomCollector(disable_target_info=disable_target_info, prefix=prefix)
         REGISTRY.register(self._collector)
         self._collector._callback = self.collect
+        self._prefix = prefix
 
     def _receive_metrics(
         self,
@@ -167,11 +168,12 @@ class _CustomCollector:
     https://github.com/prometheus/client_python#custom-collectors
     """
 
-    def __init__(self, disable_target_info: bool = False):
+    def __init__(self, disable_target_info: bool = False, prefix: str = ""):
         self._callback = None
         self._metrics_datas: Deque[MetricsData] = deque()
         self._disable_target_info = disable_target_info
         self._target_info = None
+        self._prefix = prefix
 
     def add_metrics_data(self, metrics_data: MetricsData) -> None:
         """Add metrics to Prometheus data"""
@@ -227,7 +229,10 @@ def _translate_to_prometheus(
             label_values_data_points = []
             values = []
 
-            metric_name = sanitize_full_name(metric.name)
+            metric_name = metric.name
+            if self._prefix:
+                metric_name = self._prefix + "_" + metric_name
+            metric_name = sanitize_full_name(metric_name)
             metric_description = metric.description or ""
             metric_unit = map_unit(metric.unit)
 

exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py

@@ -55,7 +55,7 @@ def setUp(self):
         )
 
     def verify_text_format(
-        self, metric: Metric, expect_prometheus_text: str
+        self, metric: Metric, expect_prometheus_text: str, prefix: str = ""
     ) -> None:
         metrics_data = MetricsData(
             resource_metrics=[
@@ -73,7 +73,7 @@ def verify_text_format(
             ]
         )
 
-        collector = _CustomCollector(disable_target_info=True)
+        collector = _CustomCollector(disable_target_info=True, prefix=prefix)
         collector.add_metrics_data(metrics_data)
         result_bytes = generate_latest(collector)
         result = result_bytes.decode("utf-8")
@@ -463,6 +463,28 @@ def test_metric_name(self):
                 """
             ),
         )
+        self.verify_text_format(
+            _generate_sum(name="test_counter_w_prefix", value=1, unit=""),
+            dedent(
+                """\
+                # HELP foo_test_counter_w_prefix_total foo
+                # TYPE foo_test_counter_w_prefix_total counter
+                foo_test_counter_w_prefix_total{a="1",b="true"} 1.0
+                """
+            ),
+            prefix="foo"
+        )
+        self.verify_text_format(
+            _generate_sum(name="test_counter_w_invalid_chars_prefix", value=1, unit=""),
+            dedent(
+                """\
+                # HELP _foo_test_counter_w_invalid_chars_prefix_total foo
+                # TYPE _foo_test_counter_w_invalid_chars_prefix_total counter
+                _foo_test_counter_w_invalid_chars_prefix_total{a="1",b="true"} 1.0
+                """
+            ),
+            prefix="#foo"
+        )
         self.verify_text_format(
             _generate_sum(name="1leading_digit", value=1, unit=""),
             dedent(