.

specreduce/utils/utils.py

@@ -119,7 +119,7 @@ def measure_cross_dispersion_profile(image, trace=None, crossdisp_axis=0,
     # determine if there is one pixel/wavelength selected or many as either a
     # list or a tuple to specify a range
     if pixel is not None:
-        if not (pixel is None) ^ (pixel_range is None):
+        if pixel_range is not None:
             raise ValueError('Both `pixel` and `pixel_range` can not be set'
                              ' simultaneously.')
         if isinstance(pixel, (int, float)):