prometheus module: add format_down config param

py3status/modules/prometheus.py

@@ -8,6 +8,8 @@
     format: Formatting of query result. Can refer to all labels from the query
         result. Query value placeholder __v.
         (default "{__v:.0f}")
+    format_down: Output if prometheus is not available
+        (default 'n/a')
     join: If query returned multiple rows, join them using this string.
         If you want to show just one, update your query.
         (default None)
@@ -53,6 +55,7 @@ class Py3status:
     # available configuration parameters
     color = None
     format = "{__v:.0f}"
+    format_down = "n/a"
     join = None
     query = None
     query_interval = 60
@@ -65,6 +68,12 @@ def prometheus(self):
         rows = self._query(self.query)
         res = []
 
+        if not rows:
+            return dict(
+                full_text=self.format_down,
+                cached_until=self.py3.time_in(self.query_interval),
+            )
+
         for row in rows:
             val = float(row["value"][1])
             if self.units: