diff --git a/py-polars/polars/datatypes/classes.py b/py-polars/polars/datatypes/classes.py
index 0c8da0ab2a0a..7c023314aa3b 100644
--- a/py-polars/polars/datatypes/classes.py
+++ b/py-polars/polars/datatypes/classes.py
@@ -84,7 +84,7 @@ def is_temporal(cls) -> bool:  # noqa: D102
         ...
 
     @classmethod
-    def is_nested(self) -> bool:  # noqa: D102
+    def is_nested(cls) -> bool:  # noqa: D102
         ...
 
 
diff --git a/py-polars/polars/series/series.py b/py-polars/polars/series/series.py
index 9d1a939dc3ac..a3aaa3d001cb 100644
--- a/py-polars/polars/series/series.py
+++ b/py-polars/polars/series/series.py
@@ -450,7 +450,7 @@ def _get_buffers(self) -> SeriesBuffers:
 
     @classmethod
     def _from_buffer(
-        self, dtype: PolarsDataType, buffer_info: BufferInfo, owner: Any
+        cls, dtype: PolarsDataType, buffer_info: BufferInfo, owner: Any
     ) -> Self:
         """
         Construct a Series from information about its underlying buffer.
@@ -478,11 +478,11 @@ def _from_buffer(
         -----
         This method is mainly intended for use with the dataframe interchange protocol.
         """
-        return self._from_pyseries(PySeries._from_buffer(dtype, buffer_info, owner))
+        return cls._from_pyseries(PySeries._from_buffer(dtype, buffer_info, owner))
 
     @classmethod
     def _from_buffers(
-        self,
+        cls,
         dtype: PolarsDataType,
         data: Series | Sequence[Series],
         validity: Series | None = None,
@@ -531,7 +531,7 @@ def _from_buffers(
             data = [s._s for s in data]
         if validity is not None:
             validity = validity._s
-        return self._from_pyseries(PySeries._from_buffers(dtype, data, validity))
+        return cls._from_pyseries(PySeries._from_buffers(dtype, data, validity))
 
     @property
     def dtype(self) -> DataType:
diff --git a/py-polars/polars/testing/__init__.py b/py-polars/polars/testing/__init__.py
index 06b4f6c91419..b5962f7fba2c 100644
--- a/py-polars/polars/testing/__init__.py
+++ b/py-polars/polars/testing/__init__.py
@@ -10,5 +10,4 @@
     "assert_frame_not_equal",
     "assert_series_equal",
     "assert_series_not_equal",
-    "_constants",
 ]