change merge validate errors to MergeError from ValueError

Author: Nick Eubank

pandas/core/reshape/merge.py

@@ -986,23 +986,23 @@ def _validate(self, validate):
         # Check data integrity
         if validate in ["one_to_one", "1:1"]:
             if not left_unique and not right_unique:
-                raise ValueError("Merge keys are not unique in either left"
+                raise MergeError("Merge keys are not unique in either left"
                                  " or right dataset; not a one-to-one merge")
             elif not left_unique:
-                raise ValueError("Merge keys are not unique in left dataset;"
+                raise MergeError("Merge keys are not unique in left dataset;"
                                  " not a one-to-one merge")
             elif not right_unique:
-                raise ValueError("Merge keys are not unique in right dataset;"
+                raise MergeError("Merge keys are not unique in right dataset;"
                                  " not a one-to-one merge")
 
         elif validate in ["one_to_many", "1:m"]:
             if not left_unique:
-                raise ValueError("Merge keys are not unique in left dataset;"
+                raise MergeError("Merge keys are not unique in left dataset;"
                                  "not a one-to-many merge")
 
         elif validate in ["many_to_one", "m:1"]:
             if not right_unique:
-                raise ValueError("Merge keys are not unique in right dataset;"
+                raise MergeError("Merge keys are not unique in right dataset;"
                                  " not a many-to-one merge")
 
         elif validate in ['many_to_many', 'm:m']:

pandas/tests/reshape/test_merge.py

@@ -789,11 +789,11 @@ def test_validation(self):
         merge(left, right_w_dups, left_index=True, right_index=True,
               validate='one_to_many')
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left, right_w_dups, left_index=True, right_index=True,
                   validate='one_to_one')
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left, right_w_dups, on='a', validate='one_to_one')
 
         # Dups on left
@@ -802,21 +802,21 @@ def test_validation(self):
         merge(left_w_dups, right, left_index=True, right_index=True,
               validate='many_to_one')
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left_w_dups, right, left_index=True, right_index=True,
                   validate='one_to_one')
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left_w_dups, right, on='a', validate='one_to_one')
 
         # Dups on both
         merge(left_w_dups, right_w_dups, on='a', validate='many_to_many')
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left_w_dups, right_w_dups, left_index=True,
                   right_index=True, validate='many_to_one')
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left_w_dups, right_w_dups, on='a',
                   validate='one_to_many')
 
@@ -842,7 +842,7 @@ def test_validation(self):
                                           'um... weasel noise?']},
                                    index=range(3))
 
-        with pytest.raises(ValueError):
+        with pytest.raises(MergeError):
             merge(left, right, on='a', validate='1:1')
 
         result = merge(left, right, on=['a', 'b'], validate='1:1')