Use mapper named argument

Author: TomAugspurger

pandas/core/frame.py

@@ -41,6 +41,7 @@
     is_datetimetz,
     is_datetime64_any_dtype,
     is_datetime64tz_dtype,
+    is_dict_like,
     is_bool_dtype,
     is_integer_dtype,
     is_float_dtype,
@@ -2904,27 +2905,30 @@ def reindex_axis(self, labels, axis=0, method=None, level=None, copy=True,
                                         limit=limit, fill_value=fill_value)
 
     @Appender(_shared_docs['rename'] % _shared_doc_kwargs)
-    def rename(self, *args, index=None, columns=None, **kwargs):
-        nargs = len(args)
-        if 'axis' in kwargs and (index is not None or columns is not None):
-            raise TypeError("Cannot specify 'index' or 'columns' and 'axis' at"
-                            " the same time. Specify either\n"
-                            "\t.rename(mapping, axis=axis), or\n"
-                            "\t.rename(index=index, columns=columns)")
-        if 'axis' in kwargs and nargs > 1:
-            raise TypeError("Cannot specify 'index', 'axis', and 'columns' at "
-                            "the same time.")
-        if nargs > 2:
-            raise TypeError("Too many positional arguments")
-
-        if nargs and index is not None:
-            raise TypeError("rename() got multiple arguments for argumnet "
-                            "'index'")
-
-        if index is None and nargs:
-            index = args[0]
-        if columns is None and nargs > 1:
-            columns = args[1]
+    def rename(self, mapper=None, index=None, columns=None, axis=None,
+               **kwargs):
+        if axis is not None:
+            axis = self._get_axis_name(axis)
+            # interpreting 'mapper' as a positional argument
+            if index is not None or columns is not None:
+                raise TypeError("Can't specify 'index' or 'columns' and 'axis'"
+                                " at the same time. Specify either\n"
+                                "\t.rename(mapper, axis=axis), or\n"
+                                "\t.rename(index=index, columns=columns)")
+            if axis == 'index':
+                index = mapper
+            elif axis == 'columns':
+                columns = mapper
+        elif all(x is not None for x in (mapper, index, columns)):
+            raise TypeError("Cannot specify all of 'mapper', 'index', and "
+                            "'columns'. Specify 'mapper' and 'axis', or "
+                            "'index' and 'columns'.")
+        elif axis is None and (mapper is not None and index is not None):
+            # Determine if they meant df.rename(idx_map, col_map)
+            if callable(index) or is_dict_like(index):
+                warnings.warn("Interpreting renaming index and columns. "
+                              "Use keyword arguments.", UserWarning)
+                index, columns = mapper, index
 
         return super(DataFrame, self).rename(index=index, columns=columns,
                                              **kwargs)

pandas/tests/frame/test_alter_axes.py

@@ -894,9 +894,6 @@ def test_rename_raises(self):
         with tm.assert_raises_regex(TypeError, None):
             df.rename(str.lower, str.lower, str.lower)
 
-        with tm.assert_raises_regex(TypeError, None):
-            df.rename(str.lower, index=str.lower)
-
     def test_assign_columns(self):
         self.frame['hi'] = 'there'
 
@@ -920,6 +917,14 @@ def test_set_index_preserve_categorical_dtype(self):
             result = result.reindex(columns=df.columns)
             tm.assert_frame_equal(result, df)
 
+    def test_ambiguous_warns(self):
+        df = pd.DataFrame({"A": [1, 2]})
+        with tm.assert_produces_warning(UserWarning):
+            df.rename(id, id)
+
+        with tm.assert_produces_warning(UserWarning):
+            df.rename({0: 10}, {"A": "B"})
+
 
 class TestIntervalIndex(object):