add metrics exporter example

Author: lzchen

articles/azure-monitor/app/api-filtering-sampling.md

@@ -422,6 +422,59 @@ tracer = Tracer(exporter=exporter, sampler=ProbabilitySampler(1.0))
 with tracer.span(name='parent'):
 response = requests.get(url='https://www.wikipedia.org/wiki/Rabbit')
 ```
+
+```python
+# Example for metrics exporter
+import time
+
+from opencensus.ext.azure import metrics_exporter
+from opencensus.stats import aggregation as aggregation_module
+from opencensus.stats import measure as measure_module
+from opencensus.stats import stats as stats_module
+from opencensus.stats import view as view_module
+from opencensus.tags import tag_map as tag_map_module
+
+stats = stats_module.stats
+view_manager = stats.view_manager
+stats_recorder = stats.stats_recorder
+
+CARROTS_MEASURE = measure_module.MeasureInt("carrots",
+                                            "number of carrots",
+                                            "carrots")
+CARROTS_VIEW = view_module.View("carrots_view",
+                                "number of carrots",
+                                [],
+                                CARROTS_MEASURE,
+                                aggregation_module.CountAggregation())
+
+# Callback function to only export the metric if value is greater than 0
+def callback_function(envelope):
+    return envelope.data.baseData.metrics[0].value > 0
+
+def main():
+    # Enable metrics
+    # Set the interval in seconds in which you want to send metrics
+    exporter = metrics_exporter.new_metrics_exporter(connection_string='InstrumentationKey=<your-instrumentation-key-here>')
+    exporter.add_telemetry_processor(callback_function)
+    view_manager.register_exporter(exporter)
+
+    view_manager.register_view(CARROTS_VIEW)
+    mmap = stats_recorder.new_measurement_map()
+    tmap = tag_map_module.TagMap()
+
+    mmap.measure_int_put(CARROTS_MEASURE, 1000)
+    mmap.record(tmap)
+    # Default export interval is every 15.0s
+    # Your application should run for at least this amount
+    # of time so the exporter will meet this interval
+    # Sleep can fulfill this
+    time.sleep(60)
+
+    print("Done recording metrics")
+
+if __name__ == "__main__":
+    main()
+```
 You can add as many processors as you like, and they are called in the order they are added. If one processor should throw an exception, it does not impact the following processors.
 
 ### Example TelemetryInitializers