fix warning message

specreduce/tracing.py

@@ -300,16 +300,17 @@ 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':
                 yy_i_above_half_max = np.sum(z_i > (z_i.max() / 2))
                 width_guess_i = yy_i_above_half_max / gaussian_sigma_to_fwhm
@@ -346,6 +347,16 @@ def __post_init__(self):
                 # TODO: implement smoothing with provided width
                 y_bins[i] = ilum2[z_i.argmax()]
 
+        # warn about fully-masked bins
+        if len(warn_bins) > 0:
+            plural = 's' if len(warn_bins) == 1 else ''
+            # 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[10: 19]
+
+            warnings.warn(f"All pixels in bin{plural} {', '.join([str(x) for x in warn_bins])} are masked. Falling "
+                              'to trace value from all-bin fit.')
+
         # recenter bin positions
         x_bins = (x_bins[:-1] + x_bins[1:]) / 2