Fix missing number in Quantity formatting for small values

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

RELEASE_NOTES.md

@@ -87,3 +87,4 @@
   A bug made the resampler interpret zero values as `None` when generating new samples, so if the result of the resampling is zero, the resampler would just produce `None` values.
 
 - The PowerManager no longer holds on to proposals from dead actors forever.  If an actor hasn't sent a new proposal in 60 seconds, the available proposal from that actor is dropped.
+- Fix `Quantity.__format__()` sometimes skipping the number for very small values.

src/frequenz/sdk/timeseries/_quantities.py

@@ -226,7 +226,12 @@ def __format__(self, __format_spec: str) -> str:
         else:
             unit = self._exponent_unit_map[unit_place]
         value_str = f"{self._base_value / 10 ** unit_place:.{precision}f}"
-        stripped = value_str.rstrip("0").rstrip(".")
+
+        if value_str != "0":
+            stripped = value_str.rstrip("0").rstrip(".")
+        else:
+            stripped = value_str
+
         if not keep_trailing_zeros:
             value_str = stripped
         unit_str = unit if stripped != "0" else self._exponent_unit_map[0]

tests/timeseries/test_quantities.py

@@ -107,6 +107,8 @@ def test_string_representation() -> None:
     )
     assert f"{Quantity(1.024445, exponent=0)}" == "1.024"
     assert f"{Quantity(1.024445, exponent=0):.0}" == "1"
+    assert f"{Quantity(0.124445, exponent=0):.0}" == "0"
+    assert f"{Quantity(0.50001, exponent=0):.0}" == "1"
     assert f"{Quantity(1.024445, exponent=0):.6}" == "1.024445"
 
     assert f"{Quantity(1.024445, exponent=3)}" == "1024.445"
@@ -128,7 +130,6 @@ def test_string_representation() -> None:
 
     assert f"{Fz1(1.024445, exponent=6)}" == "1024.445 kHz"
     assert f"{Fz2(1.024445, exponent=6)}" == "1.024 MHz"
-
     assert f"{Fz1(1.024445, exponent=9)}" == "1024445 kHz"
     assert f"{Fz2(1.024445, exponent=9)}" == "1.024 GHz"
 
@@ -147,6 +148,9 @@ def test_string_representation() -> None:
     assert f"{Fz1(-20)}" == "-20 Hz"
     assert f"{Fz1(-20000)}" == "-20 kHz"
 
+    assert f"{Power.from_watts(0.000124445):.0}" == "0 W"
+    assert f"{Energy.from_watt_hours(0.124445):.0}" == "0 Wh"
+
 
 def test_isclose() -> None:
     """Test the isclose method of the quantities."""