fix warning message

specreduce/tests/test_tracing.py

@@ -1,7 +1,8 @@
 import numpy as np
 import pytest
 from astropy.modeling import models
-
+from astropy.nddata import NDData
+import astropy.units as u
 from specreduce.utils.synth_data import make_2d_trace_image
 from specreduce.tracing import Trace, FlatTrace, ArrayTrace, FitTrace
 
@@ -148,4 +149,20 @@ def test_fit_trace():
     with pytest.raises(ValueError, match=r'image is fully masked'):
         FitTrace(img_all_nans)
 
-    # could try to catch warning thrown for all-nan bins
+    # test that warning is raised when several bins are masked
+    mask = np.zeros(img.shape)
+    mask[:, 100] = 1
+    mask[:, 20] = 1
+    mask[:, 30] = 1
+    nddat = NDData(data=img, mask=mask, unit=u.DN)
+    msg = "All pixels in bins 20, 30, 100 are masked. Falling back on trace value from all-bin fit."
+    with pytest.warns(UserWarning, match=msg):
+        FitTrace(nddat)
+
+    # and when many bins are masked
+    mask = np.zeros(img.shape)
+    mask[:, 0:21] = 1
+    nddat = NDData(data=img, mask=mask, unit=u.DN)
+    msg = 'All pixels in bins 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ..., 20 are masked.'
+    with pytest.warns(UserWarning, match=msg):
+        FitTrace(nddat)

specreduce/tracing.py

@@ -300,14 +300,14 @@ def __post_init__(self):
                              self.bins + 1, dtype=int)
         y_bins = np.tile(np.nan, self.bins)
 
+        warn_bins = []
         for i in range(self.bins):
             # repeat earlier steps to create gaussian fit for each bin
             z_i = img[ilum2, x_bins[i]:x_bins[i+1]].sum(axis=self._disp_axis)
             if not z_i.mask.all():
                 peak_y_i = ilum2[z_i.argmax()]
             else:
-                warnings.warn(f"All pixels in bin {i} are masked. Falling "
-                              'to trace value from all-bin fit.')
+                warn_bins.append(i)
                 peak_y_i = peak_y
 
             if self.peak_method == 'gaussian':
@@ -346,6 +346,15 @@ def __post_init__(self):
                 # TODO: implement smoothing with provided width
                 y_bins[i] = ilum2[z_i.argmax()]
 
+        # warn about fully-masked bins (which, currently, means any bin with a single masked value)
+        if len(warn_bins) > 0:
+            # if there are a ton of bins, we don't want to print them all out
+            if len(warn_bins) > 20:
+                warn_bins = warn_bins[0: 10] + ['...'] + [warn_bins[-1]]
+            warnings.warn(f"All pixels in {'bins' if len(warn_bins) else 'bin'} "
+                          f"{', '.join([str(x) for x in warn_bins])}"
+                          " are masked. Falling back on trace value from all-bin fit.")
+
         # recenter bin positions
         x_bins = (x_bins[:-1] + x_bins[1:]) / 2