GH20925

Raises appropriate error for Series.reset_index(level_name, drop=True) when index is flat and invalid level is supplied. Made edits as requested in the review.

Author: KalyanGokhale

pandas/core/series.py

@@ -1198,10 +1198,9 @@ def reset_index(self, level=None, drop=False, name=None, inplace=False):
             if level is not None:
                 if not isinstance(level, (tuple, list)):
                     level = [level]
-                level = set(level)
                 level = [self.index._get_level_number(lev) for lev in level]
                 if isinstance(self.index, MultiIndex):
-                    if (len(level) < len(self.index.levels)):
+                    if len(level) < self.index.nlevels:
                         new_index = self.index.droplevel(level)
 
             if inplace:

pandas/tests/series/indexing/test_indexing.py

@@ -785,8 +785,3 @@ def test_reset_index_drop_errmsg():
     # Test Case 3
     with tm.assert_raises_regex(KeyError, 'not found'):
         s.reset_index('wrong', drop=True)
-    # Data for Test Case 4
-    s = pd.Series(range(4), name='valid')
-    # Test Case 4
-    with tm.assert_raises_regex(KeyError, 'must be same as name'):
-        s.reset_index(['valid', 'valid'], drop=True)