Raise ImportError in to_pandas() and from_pandas() if pyarrow is not …

…installed. (#3348)

py-polars/polars/convert.py

@@ -248,7 +248,7 @@ def from_pandas(
     """
     Construct a Polars DataFrame or Series from a pandas DataFrame or Series.
 
-    Requires the pandas package to be installed.
+    This requires that pandas and pyarrow are installed.
 
     Parameters
     ----------
@@ -297,6 +297,11 @@ def from_pandas(
     ]
 
     """
+    if not _PYARROW_AVAILABLE:
+        raise ImportError(  # pragma: no cover
+            "'pyarrow' is required when using from_pandas()."
+        )
+
     try:
         import pandas as pd
     except ImportError as e:  # pragma: no cover

py-polars/polars/internals/frame.py

@@ -1040,7 +1040,8 @@ def to_pandas(
         self, *args: Any, date_as_object: bool = False, **kwargs: Any
     ) -> "pd.DataFrame":  # noqa: F821
         """
-        Cast to a Pandas DataFrame. This requires that Pandas is installed.
+        Cast to a pandas DataFrame.
+        This requires that pandas and pyarrow are installed.
         This operation clones data.
 
         Parameters
@@ -1068,6 +1069,10 @@ def to_pandas(
         <class 'pandas.core.frame.DataFrame'>
 
         """
+        if not _PYARROW_AVAILABLE:
+            raise ImportError(  # pragma: no cover
+                "'pyarrow' is required when using to_pandas()."
+            )
         record_batches = self._df.to_pandas()
         tbl = pa.Table.from_batches(record_batches)
         return tbl.to_pandas(*args, date_as_object=date_as_object, **kwargs)

py-polars/tests/test_interop.py

@@ -260,7 +260,7 @@ def test_from_pandas_dataframe() -> None:
     df = pl.from_pandas(pd_df)
     assert df.shape == (2, 3)
 
-    # if not a Pandas dataframe, raise a ValueError
+    # if not a pandas dataframe, raise a ValueError
     with pytest.raises(ValueError):
         _ = pl.from_pandas([1, 2])  # type: ignore