Quiet the warning of fiasco that an ion is solved with the single-ion model

utu/spectrum/_lines.py

@@ -1,6 +1,7 @@
 """The emission lines of an optically thin plasma."""
 
 import functools
+import logging
 
 import astropy.units as u
 import fiasco
@@ -245,10 +246,14 @@ def contribution_function(
 
     coupled = tuple(axis_density) == (axis_temperature,)
 
-    result = ion.contribution_function(
-        na.as_named_array(density).ndarray,
-        couple_density_to_temperature=coupled,
-    )
+    fiasco.log.addFilter(_not_single_ion)
+    try:
+        result = ion.contribution_function(
+            na.as_named_array(density).ndarray,
+            couple_density_to_temperature=coupled,
+        )
+    finally:
+        fiasco.log.removeFilter(_not_single_ion)
 
     # the last axis of the result runs over the bound-bound transitions, so
     # that is the wavelength which belongs to it
@@ -266,6 +271,20 @@ def contribution_function(
     )
 
 
+def _not_single_ion(record: logging.LogRecord) -> bool:
+    """
+    Whether a record of the log of :mod:`fiasco` is anything but its warning
+    that an ion is solved with the single-ion model.
+
+    :mod:`fiasco` asks for the two-ion model by default, and solves an ion
+    without the data that model needs with the single-ion model instead,
+    which is the right model for it. It warns each time, and that is most
+    ions, while the only way to tell which ions they are beforehand is
+    private to :mod:`fiasco`.
+    """
+    return "Using single-ion model" not in record.getMessage()
+
+
 def lines(
     temperature: na.AbstractScalar,
     density: u.Quantity | na.AbstractScalar,

utu/spectrum/_tests/test_lines.py

@@ -144,6 +144,40 @@ def test_contribution_function_grid(proton_electron_ratio: u.Quantity):
     assert shape["_density"] == 2
 
 
+@needs_database
+def test_contribution_function_single_ion(
+    caplog: pytest.LogCaptureFixture,
+    proton_electron_ratio: u.Quantity,
+):
+    """
+    An ion without the data for the two-ion model, which fiasco solves with
+    the single-ion model and warns about, is solved the same way without
+    the warning.
+    """
+    ion = fiasco.Ion("O 5", temperature.ndarray)
+
+    fiasco.log.addHandler(caplog.handler)
+    try:
+        result = utu.spectrum.contribution_function(
+            ion=ion,
+            density=density,
+            axis_temperature="temperature",
+            proton_electron_ratio=proton_electron_ratio,
+        )
+        assert not any("single-ion" in r.getMessage() for r in caplog.records)
+
+        # fiasco itself warns about this ion, once the call above is done
+        expected = ion.contribution_function(
+            density.ndarray,
+            couple_density_to_temperature=True,
+        )
+        assert any("single-ion" in r.getMessage() for r in caplog.records)
+    finally:
+        fiasco.log.removeHandler(caplog.handler)
+
+    assert np.all(result.outputs.ndarray == expected[:, 0, :])
+
+
 @needs_database
 def test_lines():
     """The whole of it, with nothing given that can be worked out."""