changes based on discussion

pandas-dev · jreback · Feb 6, 2019 · Feb 2, 2019 · Feb 2, 2019 · Feb 2, 2019
commit 3f65bf19b2739612e068c3659ba5f2d6bdd13377
diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
@@ -1967,17 +1967,6 @@ def items_overlap_with_suffix(left, lsuffix, right, rsuffix):
     if len(to_rename) == 0:
         return left, right
     else:
-        # if column name is string, raise error if suffix is a combination of
-        # empty string and None, or two Nones
-        if isinstance(to_rename[0], str):
-            if not lsuffix and not rsuffix:
-                raise ValueError('columns overlap but no suffix specified: '
-                                 '{rename}'.format(rename=to_rename))
-        else:
-            # if not, only suffix with (None, None) will raise error
-            if lsuffix is None and rsuffix is None:
-                raise ValueError('columns overlap but no suffix specified: '
-                                 '{rename}'.format(rename=to_rename))
 
         def renamer(x, suffix):
             """Rename the left and right indices.

diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
@@ -159,13 +159,12 @@ def merge_ordered(left, right, on=None,
         left DataFrame
     fill_method : {'ffill', None}, default None
         Interpolation method for data
-    suffixes : Sequence, default is ("_x", "_y")
+    suffixes : Sequence or None, default is ("_x", "_y")
         A length-2 sequence where each element is optionally a string
         indicating the suffix to add to overlapping column names in
         `left` and `right` respectively. Pass a value of `None` instead
         of a string to indicate that the column name from `left` or
-        `right` should be left as-is, with no suffix. At least one of the
-        values must not be None.
+        `right` should be left as-is, with no suffix.
     how : {'left', 'right', 'outer', 'inner'}, default 'outer'
         * left: use only keys from left frame (SQL: left outer join)
         * right: use only keys from right frame (SQL: right outer join)
@@ -493,6 +492,8 @@ def __init__(self, left, right, how='inner', on=None,
 
         self.copy = copy
         self.suffixes = suffixes
+        if suffixes is None:
+            self.suffixes = (None, None)
         self.sort = sort
 
         self.left_index = left_index

diff --git a/pandas/tests/reshape/merge/test_merge.py b/pandas/tests/reshape/merge/test_merge.py
@@ -1538,10 +1538,17 @@ def test_merge_series(on, left_on, right_on, left_index, right_index, nm):
     ("a", "a", dict(suffixes=("_x", None)), ["a_x", "a"]),
     ("a", "b", dict(suffixes=("_x", None)), ["a", "b"]),
     ("a", "a", dict(suffixes=[None, "_x"]), ["a", "a_x"]),
-    (0, 0, dict(suffixes=(["_a", None])), ["0_a", 0]),
+    (0, 0, dict(suffixes=["_a", None]), ["0_a", 0]),
     (0, 0, dict(suffixes=('', None)), ["0", 0]),
     ("a", "a", dict(), ["a_x", "a_y"]),
-    (0, 0, dict(), ["0_x", "0_y"])
+    (0, 0, dict(), ["0_x", "0_y"]),
+    ("a", "a", dict(suffixes=(None, None)), ["a", "a"]),
+    ("a", "a", dict(suffixes=[None, None]), ["a", "a"]),
+    (0, 0, dict(suffixes=(None, None)), [0, 0]),
+    ("a", "a", dict(suffixes=['', None]), ["a", "a"]),
+    (0, 0, dict(suffixes=['', None]), ["0", 0]),
+    (0, 0, dict(suffixes=None), [0, 0]),
+    ("a", "a", dict(suffixes=None), ["a", "a"])
 ])
 def test_merge_suffix(col1, col2, kwargs, expected_cols):
     # issue: 24782
@@ -1556,20 +1563,3 @@ def test_merge_suffix(col1, col2, kwargs, expected_cols):
 
     result = pd.merge(a, b, left_index=True, right_index=True, **kwargs)
     tm.assert_frame_equal(result, expected)
-
-
-@pytest.mark.parametrize("col, suffixes", [
-    ('a', (None, None)),
-    ('a', [None, None]),
-    ('a', ('', None)),
-    ('a', [None, '']),
-    (0, (None, None))
-])
-def test_merge_suffix_errors(col, suffixes):
-    # issue: 24782
-    a = pd.DataFrame({col: [1, 2, 3]})
-    b = pd.DataFrame({col: [4, 5, 6]})
-
-    with pytest.raises(ValueError,
-                       match="columns overlap but no suffix specified"):
-        a.merge(b, left_index=True, right_index=True, suffixes=suffixes)