fix: Series iteration correctly returns values instead of index (#339)

* fix: Series iteration correctly returns values instead of index

* Update iter docstring

bigframes/series.py

@@ -155,7 +155,7 @@ def __len__(self):
 
     def __iter__(self) -> typing.Iterator:
         return itertools.chain.from_iterable(
-            map(lambda x: x.index, self._block.to_pandas_batches())
+            map(lambda x: x.squeeze(axis=1), self._block.to_pandas_batches())
         )
 
     def copy(self) -> Series:

tests/system/small/test_series.py

@@ -2987,3 +2987,13 @@ def test_sample(scalars_dfs, frac, n, random_state):
     n = 1 if n is None else n
     expected_sample_size = round(frac * scalars_df.shape[0]) if frac is not None else n
     assert bf_result.shape[0] == expected_sample_size
+
+
+def test_series_iter(
+    scalars_df_index,
+    scalars_pandas_df_index,
+):
+    for bf_i, pd_i in zip(
+        scalars_df_index["int64_too"], scalars_pandas_df_index["int64_too"]
+    ):
+        assert bf_i == pd_i

third_party/bigframes_vendored/pandas/core/generic.py

@@ -50,10 +50,10 @@ def size(self) -> int:
 
     def __iter__(self) -> Iterator:
         """
-        Iterate over info axis.
+        Iterate over column axis for DataFrame, or values for Series.
 
-        Returns
-            iterator: Info axis as iterator.
+        Returns:
+            iterator
 
         **Examples:**
             >>> import bigframes.pandas as bpd
@@ -71,9 +71,9 @@ def __iter__(self) -> Iterator:
             >>> series = bpd.Series(["a", "b", "c"], index=[10, 20, 30])
             >>> for x in series:
             ...     print(x)
-            10
-            20
-            30
+            a
+            b
+            c
         """
         raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)