Print clear error messages when cannot look up things (#455)

* Print clear error messages when cannot look up things

* Spell out the failing key

ale/drivers/lro_drivers.py

@@ -573,7 +573,11 @@ class LroLrocNacIsisLabelIsisSpiceDriver(LineScanner, IsisSpice, IsisLabel, Driv
         : list
           Radial distortion coefficients. There is only one coefficient for LROC NAC l/r
         """
-        return [self.naif_keywords.get('INS{}_OD_K'.format(self.ikid), None)]
+        key = 'INS{}_OD_K'.format(self.ikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse the distortion model coefficients using key: ' + key)
+        return [ans]
 
     @property
     def detector_center_sample(self):
@@ -873,7 +877,6 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         }
         return id_lookup[super().instrument_id]
 
-
     @property
     def sensor_name(self):
         return self.label['IsisCube']['Instrument']['SpacecraftName']
@@ -940,10 +943,13 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         : list
           Radial distortion coefficients.
         """
-        coeffs = self.naif_keywords.get('INS{}_OD_K'.format(self.fikid), None)
-        coeffs = [x * -1 for x in coeffs]
-        return coeffs
+        key = 'INS{}_OD_K'.format(self.fikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse the distortion model coefficients using key: ' + key)
         
+        ans = [x * -1 for x in ans]
+        return ans
 
     @property
     def framelet_height(self):
@@ -963,8 +969,11 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         : list<double>
         detector to focal plane x
         """
-        return self.naif_keywords.get('INS{}_TRANSX'.format(self.fikid), None)
-
+        key = 'INS{}_TRANSX'.format(self.fikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse detector to focal plane x using key: ' + key)
+        return ans
 
     @property
     def pixel2focal_y(self):
@@ -976,7 +985,11 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         : list<double>
         detector to focal plane y
         """
-        return self.naif_keywords.get('INS{}_TRANSY'.format(self.fikid), None)
+        key = 'INS{}_TRANSY'.format(self.fikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse detector to focal plane y using key: ' + key)
+        return ans
 
     @property
     def focal_length(self):
@@ -992,7 +1005,11 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         float :
             The focal length in millimeters
         """
-        return self.naif_keywords.get('INS{}_FOCAL_LENGTH'.format(self.fikid), None)
+        key = 'INS{}_FOCAL_LENGTH'.format(self.fikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse the focal length using key: ' + key)
+        return ans
     
     @property
     def detector_center_sample(self):
@@ -1006,7 +1023,11 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         list :
             The center of the CCD formatted as line, sample
         """
-        return self.naif_keywords.get('INS{}_BORESIGHT_SAMPLE'.format(self.fikid), None)
+        key = 'INS{}_BORESIGHT_SAMPLE'.format(self.fikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse the detector center sample using key: ' + key)
+        return ans
 
     @property
     def detector_center_line(self):
@@ -1020,7 +1041,11 @@ class LroLrocWacIsisLabelIsisSpiceDriver(PushFrame, IsisLabel, IsisSpice, Radial
         list :
             The center of the CCD formatted as line, sample
         """
-        return self.naif_keywords.get('INS{}_BORESIGHT_LINE'.format(self.fikid), None)
+        key = 'INS{}_BORESIGHT_LINE'.format(self.fikid)
+        ans = self.naif_keywords.get(key, None)
+        if ans is None:
+            raise Exception('Could not parse the detector center line using key: ' + key)
+        return ans
 
 class LroLrocWacIsisLabelNaifSpiceDriver(PushFrame, IsisLabel, NaifSpice, RadialDistortion, Driver):
     """