Update python metrics example in programming guide (#36334)

Author: hjtran

sdks/python/apache_beam/programming_guide_test.py

@@ -0,0 +1,33 @@
+import unittest
+
+import apache_beam as beam
+from apache_beam import metrics
+from apache_beam.runners.direct.direct_runner import BundleBasedDirectRunner
+
+
+class ProgrammingGuideTest(unittest.TestCase):
+  def test_metrics_example(self):
+    class MyMetricsDoFn(beam.DoFn):
+      def __init__(self):
+        super().__init__()
+        self.counter = metrics.Metrics.counter("namespace", "counter1")
+
+      def process(self, element):
+        self.counter.inc()
+        yield element
+
+    with beam.Pipeline(runner=BundleBasedDirectRunner()) as p:
+      _ = (p | beam.Create([1, 2, 3]) | beam.ParDo(MyMetricsDoFn()))
+
+    metrics_filter = metrics.MetricsFilter().with_name("counter1")
+    query_result = p.result.metrics().query(metrics_filter)
+
+    for metric in query_result["counters"]:
+      print(metric)
+
+    # Not in example but just to confirm that anything is returned
+    assert query_result["counters"]
+
+
+if __name__ == '__main__':
+  unittest.main()

website/www/site/content/en/documentation/programming-guide.md

@@ -6422,22 +6422,20 @@ public class MyMetricsDoFn extends DoFn<Integer, Integer> {
 {{< highlight py >}}
 class MyMetricsDoFn(beam.DoFn):
   def __init__(self):
+    super().__init__()
     self.counter = metrics.Metrics.counter("namespace", "counter1")
 
   def process(self, element):
-    counter.inc()
+    self.counter.inc()
     yield element
 
-pipeline = beam.Pipeline()
-
-pipeline | beam.ParDo(MyMetricsDoFn())
-
-result = pipeline.run().wait_until_finish()
+with beam.Pipeline() as p:
+  p | beam.Create([1, 2, 3]) | beam.ParDo(MyMetricsDoFn())
 
-metrics = result.metrics().query(
-    metrics.MetricsFilter.with_namespace("namespace").with_name("counter1"))
+metrics_filter = metrics.MetricsFilter().with_name("counter1")
+query_result  = p.result.metrics().query(metrics_filter)
 
-for metric in metrics["counters"]:
+for metric in query_result["counters"]:
   print(metric)
 {{< /highlight >}}