Make slicing a series raise a not implemented error (#469)

dask_expr/_collection.py

@@ -154,6 +154,8 @@ def __reduce__(self):
     def __getitem__(self, other):
         if isinstance(other, FrameBase):
             return new_collection(self.expr.__getitem__(other.expr))
+        elif isinstance(other, slice):
+            return self.loc[other]
         return new_collection(self.expr.__getitem__(other))
 
     def persist(self, fuse=True, combine_similar=True, **kwargs):

dask_expr/_expr.py

@@ -1991,7 +1991,7 @@ def _meta(self):
         if is_dataframe_like(self.frame._meta):
             return super()._meta
         # if we are not a DataFrame and have a scalar, we reduce to a scalar
-        if not isinstance(self.operand("columns"), list) and not hasattr(
+        if not isinstance(self.operand("columns"), (list, slice)) and not hasattr(
             self.operand("columns"), "dtype"
         ):
             return meta_nonempty(self.frame._meta).iloc[0]

dask_expr/tests/test_collection.py

@@ -1052,6 +1052,11 @@ def test_dropna_simplify(pdf, subset):
     assert_eq(q, pdf.dropna(subset=subset)["y"])
 
 
+def test_series_slice_getitem(df, pdf):
+    with pytest.raises(NotImplementedError):
+        df.x[:4]
+
+
 def test_dir(df):
     assert all(c in dir(df) for c in df.columns)
     assert "sum" in dir(df)