edit error message

Author: yucongalicechen

src/diffpy/utils/scattering_objects/diffraction_objects.py

@@ -783,9 +783,7 @@ def q_to_tth(self):
         wavelength = float(self.wavelength)
         pre_factor = wavelength / (4 * np.pi)
         if np.any(np.abs(q * pre_factor) > 1):
-            raise ValueError(
-                "Invalid input for arcsin: some values exceed the range [-1, 1]. Check wavelength or q values."
-            )
+            raise ValueError("Please check if you entered an incorrect wavelength or q value.")
         return np.rad2deg(2.0 * np.arcsin(q * pre_factor))
 
     def tth_to_q(self):
@@ -822,7 +820,10 @@ def tth_to_q(self):
         """
         two_theta = np.asarray(np.deg2rad(self.on_tth[0]))
         if np.any(two_theta > np.pi):
-            raise ValueError("Two theta exceeds 180 degrees.")
+            raise ValueError(
+                "Two theta exceeds 180 degrees. Please check if invalid values were entered "
+                "or if degrees were incorrectly specified as radians."
+            )
         wavelength = float(self.wavelength)
         pre_factor = (4 * np.pi) / wavelength
         return pre_factor * np.sin(two_theta / 2)

tests/diffpy/utils/scattering_objects/test_diffraction_objects.py

@@ -232,7 +232,7 @@ def test_diffraction_objects_equality(inputs1, inputs2, expected):
 
 
 def test_q_to_tth():
-    # valid q values including edge cases when q=0 or 1
+    # valid q values including edge cases when q=0 or tth=180 after converting
     # expected tth values are 2*arcsin(q)
     actual = DiffractionObject(wavelength=4 * np.pi)
     setattr(actual, "on_q", [[0, 0.2, 0.4, 0.6, 0.8, 1], [1, 2, 3, 4, 5, 6]])
@@ -242,7 +242,7 @@ def test_q_to_tth():
 
 
 def test_q_to_tth_bad():
-    # invalid q values when arcsin value is not in the range of [-1, 1]
+    # invalid wavelength or q values when arcsin value is not in the range of [-1, 1]
     actual = DiffractionObject(wavelength=4 * np.pi)
     setattr(actual, "on_q", [[0.6, 0.8, 1, 1.2], [1, 2, 3, 4]])
     with pytest.raises(ValueError):