feat: support astype to json (#2073)

Author: chelsea-lin

bigframes/dtypes.py

@@ -641,6 +641,9 @@ def _dtype_from_string(dtype_string: str) -> typing.Optional[Dtype]:
         return BIGFRAMES_STRING_TO_BIGFRAMES[
             typing.cast(DtypeString, str(dtype_string))
         ]
+    if isinstance(dtype_string, str) and dtype_string.lower() == "json":
+        return JSON_DTYPE
+
     raise TypeError(
         textwrap.dedent(
             f"""
@@ -652,9 +655,9 @@ def _dtype_from_string(dtype_string: str) -> typing.Optional[Dtype]:
                         The following pandas.ExtensionDtype are supported:
                         pandas.BooleanDtype(), pandas.Float64Dtype(),
                         pandas.Int64Dtype(), pandas.StringDtype(storage="pyarrow"),
-                        pd.ArrowDtype(pa.date32()), pd.ArrowDtype(pa.time64("us")),
-                        pd.ArrowDtype(pa.timestamp("us")),
-                        pd.ArrowDtype(pa.timestamp("us", tz="UTC")).
+                        pandas.ArrowDtype(pa.date32()), pandas.ArrowDtype(pa.time64("us")),
+                        pandas.ArrowDtype(pa.timestamp("us")),
+                        pandas.ArrowDtype(pa.timestamp("us", tz="UTC")).
                 {constants.FEEDBACK_LINK}
                 """
         )

tests/system/small/test_series.py

@@ -3903,6 +3903,18 @@ def test_float_astype_json(errors):
     pd.testing.assert_series_equal(bf_result.to_pandas(), expected_result)
 
 
+def test_float_astype_json_str():
+    data = ["1.25", "2500000000", None, "-12323.24"]
+    bf_series = series.Series(data, dtype=dtypes.FLOAT_DTYPE)
+
+    bf_result = bf_series.astype("json")
+    assert bf_result.dtype == dtypes.JSON_DTYPE
+
+    expected_result = pd.Series(data, dtype=dtypes.JSON_DTYPE)
+    expected_result.index = expected_result.index.astype("Int64")
+    pd.testing.assert_series_equal(bf_result.to_pandas(), expected_result)
+
+
 @pytest.mark.parametrize("errors", ["raise", "null"])
 def test_string_astype_json(errors):
     data = [