improving error handling for case where a variable is missing

pyspedas/mms/fgm/mms_curl.py

@@ -65,21 +65,57 @@ def mms_curl(fields=None, positions=None, suffix=''):
 
     m0 = 4.0*math.pi*1e-7
 
-    timesb1, datab1 = get_data(fields[0])
-    timesb2, datab2 = get_data(fields[1] + '_i')
-    timesb3, datab3 = get_data(fields[2] + '_i')
-    timesb4, datab4 = get_data(fields[3] + '_i')
+    mms1_bfield = get_data(fields[0])
+    mms2_bfield = get_data(fields[1] + '_i')
+    mms3_bfield = get_data(fields[2] + '_i')
+    mms4_bfield = get_data(fields[3] + '_i')
+
+    if mms1_bfield is None:
+        print('Error, B-field variable is missing: ' + fields[0])
+        return
+    elif mms2_bfield is None:
+        print('Error, B-field variable is missing: ' + fields[1] + '_i')
+        return
+    elif mms3_bfield is None:
+        print('Error, B-field variable is missing: ' + fields[2] + '_i')
+        return
+    elif mms4_bfield is None:
+        print('Error, B-field variable is missing: ' + fields[3] + '_i')
+        return
+
+    timesb1, datab1 = mms1_bfield
+    timesb2, datab2 = mms2_bfield
+    timesb3, datab3 = mms3_bfield
+    timesb4, datab4 = mms4_bfield
 
     # extract the vector
     b1 = datab1[:, 0:3]
     b2 = datab2[:, 0:3]
     b3 = datab3[:, 0:3]
     b4 = datab4[:, 0:3]
 
-    timesp1, p1 = get_data(positions[0] + '_i')
-    timesp2, p2 = get_data(positions[1] + '_i')
-    timesp3, p3 = get_data(positions[2] + '_i')
-    timesp4, p4 = get_data(positions[3] + '_i')
+    mms1_pos = get_data(positions[0] + '_i')
+    mms2_pos = get_data(positions[1] + '_i')
+    mms3_pos = get_data(positions[2] + '_i')
+    mms4_pos = get_data(positions[3] + '_i')
+
+    if mms1_pos is None:
+        print('Error, S/C position variable is missing: ' + positions[0] + '_i')
+        return
+    elif mms2_pos is None:
+        print('Error, S/C position variable is missing: ' + positions[1] + '_i')
+        return
+    elif mms3_pos is None:
+        print('Error, S/C position variable is missing: ' + positions[2] + '_i')
+        return
+    elif mms4_pos is None:
+        print('Error, S/C position variable is missing: ' + positions[3] + '_i')
+        return
+
+    timesp1, p1 = mms1_pos
+    timesp2, p2 = mms2_pos
+    timesp3, p3 = mms3_pos
+    timesp4, p4 = mms4_pos
 
     divb = np.zeros([len(timesb1), 5])
     baryb = np.zeros([len(timesb1), 3])