chore: remove initialization workaround in to_datetime. (#514)

* chore: Remove initialization workaround in to_datetime.

* remove unused import

* Update document.

Author: Genesis929

bigframes/core/tools/datetimes.py

@@ -20,7 +20,6 @@
 import pandas as pd
 
 import bigframes.constants as constants
-import bigframes.core.global_session as global_session
 import bigframes.dataframe
 import bigframes.operations as ops
 import bigframes.series
@@ -52,21 +51,7 @@ def to_datetime(
             f"to datetime is not implemented. {constants.FEEDBACK_LINK}"
         )
 
-    if not isinstance(arg, bigframes.series.Series):
-        # This block ensures compatibility with local data formats, including
-        # iterables and pandas.Series
-        # TODO: Currently, data upload is performed using pandas DataFrames
-        # combined with the `read_pandas` method due to the BigFrames DataFrame
-        # constructor's limitations in handling various data types. Plan to update
-        # the upload process to utilize the BigFrames DataFrame constructor directly
-        # once it is enhanced for more related datatypes.
-        arg = global_session.with_default_session(
-            bigframes.session.Session.read_pandas, pd.DataFrame(arg)
-        )
-        if len(arg.columns) != 1:
-            raise ValueError("Input must be 1-dimensional.")
-
-        arg = arg[arg.columns[0]]
+    arg = bigframes.series.Series(arg)
 
     if not utc and arg.dtype not in ("Int64", "Float64"):  # type: ignore
         raise NotImplementedError(

third_party/bigframes_vendored/pandas/core/arrays/datetimelike.py

@@ -26,7 +26,7 @@ def strftime(self, date_format: str):
             0      August 15, 2014, 08:15:12 AM
             1    February 29, 2012, 02:15:12 AM
             2      August 15, 2015, 03:15:12 AM
-            Name: 0, dtype: string
+            dtype: string
 
         Args:
             date_format (str):

third_party/bigframes_vendored/pandas/core/tools/datetimes.py

@@ -48,7 +48,7 @@ def to_datetime(
         >>> bpd.to_datetime(list_str, format="%m-%d-%Y %H:%M", utc=True)
         0    2021-01-31 14:30:00+00:00
         1    2021-02-28 15:45:00+00:00
-        Name: 0, dtype: timestamp[us, tz=UTC][pyarrow]
+        dtype: timestamp[us, tz=UTC][pyarrow]
 
     Converting a Series of Strings with Timezone Information: