BUG: Fix get dummies unicode error (pandas-dev#22131)

Author: Scorpil

doc/source/whatsnew/v0.24.0.txt

@@ -660,6 +660,7 @@ Reshaping
 - Bug in :meth:`Series.mask` and :meth:`DataFrame.mask` with ``list`` conditionals (:issue:`21891`)
 - Bug in :meth:`DataFrame.replace` raises RecursionError when converting OutOfBounds ``datetime64[ns, tz]`` (:issue:`20380`)
 - :func:`pandas.core.groupby.GroupBy.rank` now raises a ``ValueError`` when an invalid value is passed for argument ``na_option`` (:issue:`22124`)
+- Bug in :func:`get_dummies` with Unicode attributes in Python 2 (:issue:`22084`)
 -
 
 Build Changes

pandas/core/reshape/reshape.py

@@ -1,6 +1,6 @@
 # pylint: disable=E1101,E1103
 # pylint: disable=W0703,W0622,W0613,W0201
-from pandas.compat import range, text_type, zip
+from pandas.compat import range, text_type, zip, u, PY2
 from pandas import compat
 from functools import partial
 import itertools
@@ -923,13 +923,23 @@ def get_empty_Frame(data, sparse):
 
     number_of_cols = len(levels)
 
-    if prefix is not None:
-        dummy_strs = [u'{prefix}{sep}{level}' if isinstance(v, text_type)
-                      else '{prefix}{sep}{level}' for v in levels]
-        dummy_cols = [dummy_str.format(prefix=prefix, sep=prefix_sep, level=v)
-                      for dummy_str, v in zip(dummy_strs, levels)]
-    else:
+    if prefix is None:
         dummy_cols = levels
+    else:
+
+        # PY2 embedded unicode, gh-22084
+        def _make_col_name(prefix, prefix_sep, level):
+            fstr = '{prefix}{prefix_sep}{level}'
+            if PY2 and (isinstance(prefix, text_type) or
+                        isinstance(prefix_sep, text_type) or
+                        isinstance(level, text_type)):
+                fstr = u(fstr)
+            return fstr.format(prefix=prefix,
+                               prefix_sep=prefix_sep,
+                               level=level)
+
+        dummy_cols = [_make_col_name(prefix, prefix_sep, level)
+                      for level in levels]
 
     if isinstance(data, Series):
         index = data.index

pandas/tests/reshape/test_reshape.py

@@ -302,6 +302,24 @@ def test_dataframe_dummies_with_categorical(self, df, sparse, dtype):
         expected.sort_index(axis=1)
         assert_frame_equal(result, expected)
 
+    @pytest.mark.parametrize('get_dummies_kwargs,expected', [
+        ({'data': pd.DataFrame(({u'ä': ['a']}))},
+         pd.DataFrame({u'ä_a': [1]}, dtype=np.uint8)),
+
+        ({'data': pd.DataFrame({'x': [u'ä']})},
+         pd.DataFrame({u'x_ä': [1]}, dtype=np.uint8)),
+
+        ({'data': pd.DataFrame({'x': [u'a']}), 'prefix':u'ä'},
+         pd.DataFrame({u'ä_a': [1]}, dtype=np.uint8)),
+
+        ({'data': pd.DataFrame({'x': [u'a']}), 'prefix_sep':u'ä'},
+         pd.DataFrame({u'xäa': [1]}, dtype=np.uint8))])
+    def test_dataframe_dummies_unicode(self, get_dummies_kwargs, expected):
+        # GH22084 pd.get_dummies incorrectly encodes unicode characters
+        # in dataframe column names
+        result = get_dummies(**get_dummies_kwargs)
+        assert_frame_equal(result, expected)
+
     def test_basic_drop_first(self, sparse):
         # GH12402 Add a new parameter `drop_first` to avoid collinearity
         # Basic case