convert non-string colnames to strings in interchange protocol

Author: MarcoGorelli

doc/source/whatsnew/v2.2.1.rst

@@ -29,6 +29,7 @@ Fixed regressions
 
 Bug fixes
 ~~~~~~~~~
+- Fixed bug in :func:`pandas.api.interchange.from_dataframe` which wasn't converting columns names to strings (:issue:`55069`)
 - Fixed bug in :meth:`DataFrame.__getitem__` for empty :class:`DataFrame` with Copy-on-Write enabled (:issue:`57130`)
 
 .. ---------------------------------------------------------------------------

pandas/core/interchange/dataframe.py

@@ -32,7 +32,7 @@ def __init__(self, df: DataFrame, allow_copy: bool = True) -> None:
         Constructor - an instance of this (private) class is returned from
         `pd.DataFrame.__dataframe__`.
         """
-        self._df = df
+        self._df = df.rename(columns=str, copy=False)
         self._allow_copy = allow_copy
 
     def __dataframe__(

pandas/tests/interchange/test_impl.py

@@ -392,3 +392,22 @@ def test_large_string():
     result = pd.api.interchange.from_dataframe(df.__dataframe__())
     expected = pd.DataFrame({"a": ["x"]}, dtype="object")
     tm.assert_frame_equal(result, expected)
+<<<<<<< HEAD
+=======
+
+
+@pytest.mark.parametrize("dtype", ["Int8", "Int8[pyarrow]"])
+def test_nullable_integers(dtype: str) -> None:
+    pytest.importorskip("pyarrow")
+    df = pd.DataFrame({"a": [1]}, dtype=dtype)
+    expected = pd.DataFrame({"a": [1]}, dtype="int8")
+    result = pd.api.interchange.from_dataframe(df.__dataframe__())
+    tm.assert_frame_equal(result, expected)
+
+
+def test_non_str_names():
+    # https://github.com/pandas-dev/pandas/issues/56701
+    df = pd.Series([1, 2, 3], name=0).to_frame()
+    names = df.__dataframe__().column_names()
+    assert names == ["0"]
+>>>>>>> 2383e4b049 (wip)