Handle NaN/INF values in FormulaEngine

The MetricFetcher propagates NaN to handle None values
when None values are not treat from the stream as 0s.
So that any FormulaStep can compute the results without
checking for None on each value involved in the FormulaStep.
However the final result is written as None rather than NaN/INF
in the FormulaEngine.

Signed-off-by: Daniel Zullo <[email protected]>

Author: daniel-zullo-frequenz

src/frequenz/sdk/timeseries/logical_meter/_formula_engine.py

@@ -10,6 +10,7 @@
 import weakref
 from collections import deque
 from datetime import datetime
+from math import isinf, isnan
 from typing import Dict, List, Optional, Set, Tuple
 from uuid import UUID, uuid4
 
@@ -154,7 +155,11 @@ async def _apply(self) -> Sample:
         if len(eval_stack) != 1:
             raise RuntimeError(f"Formula application failed: {self._name}")
 
-        return Sample(metric_ts, eval_stack[0])
+        res = eval_stack.pop()
+        if isnan(res) or isinf(res):
+            res = None
+
+        return Sample(metric_ts, res)
 
     async def _run(self) -> None:
         sender = self._channel.new_sender()

src/frequenz/sdk/timeseries/logical_meter/_formula_steps.py

@@ -6,6 +6,7 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
+from math import isinf, isnan
 from typing import List, Optional
 
 from frequenz.channels import Receiver
@@ -57,10 +58,7 @@ def apply(self, eval_stack: List[Optional[float]]) -> None:
         """
         val2 = eval_stack.pop()
         val1 = eval_stack.pop()
-        if val1 is None or val2 is None:
-            res = None
-        else:
-            res = val1 + val2
+        res = val1 + val2
         eval_stack.append(res)
 
 
@@ -83,10 +81,7 @@ def apply(self, eval_stack: List[Optional[float]]) -> None:
         """
         val2 = eval_stack.pop()
         val1 = eval_stack.pop()
-        if val1 is None or val2 is None:
-            res = None
-        else:
-            res = val1 - val2
+        res = val1 - val2
         eval_stack.append(res)
 
 
@@ -109,10 +104,7 @@ def apply(self, eval_stack: List[Optional[float]]) -> None:
         """
         val2 = eval_stack.pop()
         val1 = eval_stack.pop()
-        if val1 is None or val2 is None:
-            res = None
-        else:
-            res = val1 * val2
+        res = val1 * val2
         eval_stack.append(res)
 
 
@@ -135,10 +127,7 @@ def apply(self, eval_stack: List[Optional[float]]) -> None:
         """
         val2 = eval_stack.pop()
         val1 = eval_stack.pop()
-        if val1 is None or val2 is None:
-            res = None
-        else:
-            res = val1 / val2
+        res = val1 / val2
         eval_stack.append(res)
 
 
@@ -265,7 +254,12 @@ def apply(self, eval_stack: List[Optional[float]]) -> None:
         """
         if self._next_value is None:
             raise RuntimeError("No next value available to append.")
-        if self._next_value.value is None and self._nones_are_zeros:
-            eval_stack.append(0.0)
+
+        next_value = self._next_value.value
+        if next_value is None or isnan(next_value) or isinf(next_value):
+            if self._nones_are_zeros:
+                eval_stack.append(0.0)
+            else:
+                eval_stack.append(float("NaN"))
         else:
             eval_stack.append(self._next_value.value)