feat: add Series.struct.dtypes property (#599)

Author: chelsea-lin

bigframes/operations/structs.py

@@ -15,9 +15,11 @@
 from __future__ import annotations
 
 import bigframes_vendored.pandas.core.arrays.arrow.accessors as vendoracessors
+import pandas as pd
 
 from bigframes.core import log_adapter
 import bigframes.dataframe
+import bigframes.dtypes
 import bigframes.operations
 import bigframes.operations.base
 import bigframes.series
@@ -45,3 +47,13 @@ def explode(self) -> bigframes.dataframe.DataFrame:
         return bigframes.pandas.concat(
             [self.field(i) for i in range(pa_type.num_fields)], axis="columns"
         )
+
+    def dtypes(self) -> pd.Series:
+        pa_type = self._dtype.pyarrow_dtype
+        return pd.Series(
+            data=[
+                bigframes.dtypes.arrow_dtype_to_bigframes_dtype(pa_type.field(i).type)
+                for i in range(pa_type.num_fields)
+            ],
+            index=[pa_type.field(i).name for i in range(pa_type.num_fields)],
+        )

third_party/bigframes_vendored/pandas/core/arrays/arrow/accessors.py

@@ -92,3 +92,32 @@ def explode(self):
                 The data corresponding to all child fields.
         """
         raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
+
+    def dtypes(self):
+        """
+        Return the dtype object of each child field of the struct.
+
+        **Examples:**
+
+            >>> import bigframes.pandas as bpd
+            >>> import pyarrow as pa
+            >>> bpd.options.display.progress_bar = None
+            >>> s = bpd.Series(
+            ...     [
+            ...         {"version": 1, "project": "pandas"},
+            ...         {"version": 2, "project": "pandas"},
+            ...         {"version": 1, "project": "numpy"},
+            ...     ],
+            ...     dtype=bpd.ArrowDtype(pa.struct(
+            ...         [("version", pa.int64()), ("project", pa.string())]
+            ...     ))
+            ... )
+            >>> s.struct.dtypes()
+            version              Int64
+            project    string[pyarrow]
+            dtype: object
+
+        Returns:
+            A *pandas* Series with the data type of all child fields.
+        """
+        raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)