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| 1 | +--- |
| 2 | +title: Custom Collectors |
| 3 | +weight: 1 |
| 4 | +--- |
| 5 | + |
| 6 | +Sometimes it is not possible to directly instrument code, as it is not |
| 7 | +in your control. This requires you to proxy metrics from other systems. |
| 8 | + |
| 9 | +To do so you need to create a custom collector, for example: |
| 10 | + |
| 11 | +```python |
| 12 | +from prometheus_client.core import GaugeMetricFamily, CounterMetricFamily, REGISTRY |
| 13 | +from prometheus_client.registry import Collector |
| 14 | + |
| 15 | +class CustomCollector(Collector): |
| 16 | + def collect(self): |
| 17 | + yield GaugeMetricFamily('my_gauge', 'Help text', value=7) |
| 18 | + c = CounterMetricFamily('my_counter_total', 'Help text', labels=['foo']) |
| 19 | + c.add_metric(['bar'], 1.7) |
| 20 | + c.add_metric(['baz'], 3.8) |
| 21 | + yield c |
| 22 | + |
| 23 | +REGISTRY.register(CustomCollector()) |
| 24 | +``` |
| 25 | + |
| 26 | +`SummaryMetricFamily`, `HistogramMetricFamily` and `InfoMetricFamily` work similarly. |
| 27 | + |
| 28 | +A collector may implement a `describe` method which returns metrics in the same |
| 29 | +format as `collect` (though you don't have to include the samples). This is |
| 30 | +used to predetermine the names of time series a `CollectorRegistry` exposes and |
| 31 | +thus to detect collisions and duplicate registrations. |
| 32 | + |
| 33 | +Usually custom collectors do not have to implement `describe`. If `describe` is |
| 34 | +not implemented and the CollectorRegistry was created with `auto_describe=True` |
| 35 | +(which is the case for the default registry) then `collect` will be called at |
| 36 | +registration time instead of `describe`. If this could cause problems, either |
| 37 | +implement a proper `describe`, or if that's not practical have `describe` |
| 38 | +return an empty list. |
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