FITS spec I/O col lookup is case-insensitive

again.

CHANGES.rst

@@ -5,8 +5,7 @@
   ensure that the correct ``TUNITn`` is read. As a result, ``wave_unit`` and
   ``flux_unit`` keywords are deprecated and no longer used in that function.
   Additionally, if any ``TUNITn`` in the table is invalid, regardless whether
-  the column is used or not, an exception will now be raised. The inputs
-  for ``wave_col`` and ``flux_col`` are now case-sensitive. [#384]
+  the column is used or not, an exception will now be raised. [#384]
 
 - ``read_spec()`` now detects whether given filename is FITS more consistently
   w.r.t. ``astropy``. [#384]

synphot/specio.py

@@ -167,7 +167,7 @@ def read_fits_spec(filename, ext=1, wave_col='WAVELENGTH', flux_col='FLUX',
         FITS extension with table data. Default is 1.
 
     wave_col, flux_col : str
-        Wavelength and flux column names (case-sensitive).
+        Wavelength and flux column names (case-insensitive).
 
     wave_unit, flux_unit : str or `~astropy.units.Unit`
         Wavelength and flux units. These are *no longer used*.
@@ -185,6 +185,9 @@ def read_fits_spec(filename, ext=1, wave_col='WAVELENGTH', flux_col='FLUX',
         Wavelength and flux of the spectrum.
 
     """
+    wave_col = wave_col.lower()
+    flux_col = flux_col.lower()
+
     try:
         fs = fits.open(filename)
         subhdu = fs[ext]
@@ -199,9 +202,12 @@ def read_fits_spec(filename, ext=1, wave_col='WAVELENGTH', flux_col='FLUX',
 
         t = QTable.read(subhdu)
         header = dict(fs["PRIMARY"].header)
-        t_col_wave = t[wave_col]
+
+        # https://github.com/astropy/astropy/issues/16221
+        lower_colnames = [c.lower() for c in t.colnames]
+        t_col_wave = t.columns[lower_colnames.index(wave_col)]
+        t_col_flux = t.columns[lower_colnames.index(flux_col)]
         wavelengths = t_col_wave.value * (t_col_wave.unit or u.dimensionless_unscaled)  # noqa: E501
-        t_col_flux = t[flux_col]
         fluxes = t_col_flux.value * (t_col_flux.unit or u.dimensionless_unscaled)  # noqa: E501
 
     finally:

synphot/tests/test_specio.py

@@ -158,18 +158,24 @@ def test_read_nonstandard_fits_cols_01(tmp_path):
     trace = np.array([0, 0.5, 1, 0.9, 0])
     coldefs = fits.ColDefs([
         fits.Column(name="X", format="I", array=pix),
-        fits.Column(name="WAVELENGTH", format="E",
+        fits.Column(name="Wavelength", format="E",
                     unit=wav.unit.to_string(format="fits"), array=wav.value),
-        fits.Column(name="TRACE", format="E", array=trace)])
+        fits.Column(name="Trace", format="E", array=trace)])
     hdulist = fits.HDUList([
         fits.PrimaryHDU(),
         fits.BinTableHDU.from_columns(coldefs)])
     outfile = str(tmp_path / "jwst_niriss_soss_trace.fits")
     hdulist.writeto(outfile, overwrite=True)
 
-    tr = SpectralElement.from_file(outfile, flux_col="TRACE")
-    assert_quantity_allclose(tr.waveset, wav)
-    assert_quantity_allclose(tr(wav), trace, atol=1e-7)
+    # Make sure column names are still case insensitive.
+    for (wave_col, flux_col) in (
+            ("Wavelength", "Trace"),
+            ("WAVELENGTH", "TRACE"),
+            ("wavelength", "trace")):
+        tr = SpectralElement.from_file(
+            outfile, wave_col=wave_col, flux_col=flux_col)
+        assert_quantity_allclose(tr.waveset, wav)
+        assert_quantity_allclose(tr(wav), trace, atol=1e-7)
 
 
 def test_read_nonstandard_fits_cols_02(tmp_path):