doc: show timezone conversions for timestamp columns

Pandas doesn't automatically convert datetime objects to UTC time, so
show how to do this in the code sample.

bigquery/samples/load_table_dataframe.py

@@ -33,36 +33,36 @@ def load_table_dataframe(client, table_id):
             "title": u"The Meaning of Life",
             "release_year": 1983,
             "length_minutes": 112.5,
-            "release_date": datetime.datetime(
-                1983, 5, 9, 13, 0, 0, tzinfo=pytz.timezone("Europe/Paris")
-            ),
+            "release_date": pytz.timezone("Europe/Paris")
+            .localize(datetime.datetime(1983, 5, 9, 13, 0, 0))
+            .astimezone(pytz.utc),
             "dvd_release": datetime.datetime(2002, 1, 22, 7, 0, 0),
         },
         {
             "title": u"Monty Python and the Holy Grail",
             "release_year": 1975,
             "length_minutes": 91.5,
-            "release_date": datetime.datetime(
-                1975, 4, 9, 23, 59, 2, tzinfo=pytz.timezone("Europe/London")
-            ),
+            "release_date": pytz.timezone("Europe/London")
+            .localize(datetime.datetime(1975, 4, 9, 23, 59, 2))
+            .astimezone(pytz.utc),
             "dvd_release": datetime.datetime(2002, 7, 16, 9, 0, 0),
         },
         {
             "title": u"Life of Brian",
             "release_year": 1979,
             "length_minutes": 94.25,
-            "release_date": datetime.datetime(
-                1979, 8, 17, 23, 59, 5, tzinfo=pytz.timezone("America/New_York")
-            ),
+            "release_date": pytz.timezone("America/New_York")
+            .localize(datetime.datetime(1979, 8, 17, 23, 59, 5))
+            .astimezone(pytz.utc),
             "dvd_release": datetime.datetime(2008, 1, 14, 8, 0, 0),
         },
         {
             "title": u"And Now for Something Completely Different",
             "release_year": 1971,
             "length_minutes": 88.0,
-            "release_date": datetime.datetime(
-                1971, 9, 28, 23, 59, 7, tzinfo=pytz.timezone("Europe/London")
-            ),
+            "release_date": pytz.timezone("Europe/London")
+            .localize(datetime.datetime(1971, 9, 28, 23, 59, 7))
+            .astimezone(pytz.utc),
             "dvd_release": datetime.datetime(2003, 10, 22, 10, 0, 0),
         },
     ]

bigquery/samples/tests/test_load_table_dataframe.py

@@ -59,33 +59,18 @@ def test_load_table_dataframe(capsys, client, random_table_id):
         u"Life of Brian",
         u"The Meaning of Life",
     ]
-    assert df["release_year"].tolist() == [
-        1971,
-        1975,
-        1979,
-        1983,
-    ]
-    assert df["length_minutes"].tolist() == [
-        88.0,
-        91.5,
-        94.25,
-        112.5,
-    ]
+    assert df["release_year"].tolist() == [1971, 1975, 1979, 1983]
+    assert df["length_minutes"].tolist() == [88.0, 91.5, 94.25, 112.5]
     assert df["release_date"].tolist() == [
-        pandas.Timestamp("1971-09-28T23:59:07+00:00"),
-        pandas.Timestamp("1975-04-09T23:59:02+00:00"),
-        pandas.Timestamp("1979-08-17T23:59:05+00:00"),
-        pandas.Timestamp("1983-05-09T13:00:00+00:00"),
+        pandas.Timestamp("1971-09-28T22:59:07+00:00"),
+        pandas.Timestamp("1975-04-09T22:59:02+00:00"),
+        pandas.Timestamp("1979-08-18T03:59:05+00:00"),
+        pandas.Timestamp("1983-05-09T11:00:00+00:00"),
     ]
     assert df["dvd_release"].tolist() == [
         pandas.Timestamp("2003-10-22T10:00:00+00:00"),
         pandas.Timestamp("2002-07-16T09:00:00+00:00"),
         pandas.Timestamp("2008-01-14T08:00:00+00:00"),
         pandas.Timestamp("2002-01-22T07:00:00+00:00"),
     ]
-    assert df["wikidata_id"].tolist() == [
-        u"Q16403",
-        u"Q25043",
-        u"Q24953",
-        u"Q24980",
-    ]
+    assert df["wikidata_id"].tolist() == [u"Q16403", u"Q25043", u"Q24953", u"Q24980"]

bigquery/tests/system.py

@@ -719,7 +719,12 @@ def test_load_table_from_dataframe_w_automatic_schema(self):
             (
                 bigquery.SchemaField("bool_col", "BOOLEAN"),
                 bigquery.SchemaField("ts_col", "TIMESTAMP"),
-                bigquery.SchemaField("dt_col", "DATETIME"),
+                # Due to internal bug 147108331, BigQuery always interprets
+                # DATETIME columns as having the wrong precision. In the
+                # meantime, workaround this by writing the values as TIMESTAMP.
+                # See:
+                # https://github.com/googleapis/google-cloud-python/issues/9996
+                bigquery.SchemaField("dt_col", "TIMESTAMP"),
                 bigquery.SchemaField("float32_col", "FLOAT"),
                 bigquery.SchemaField("float64_col", "FLOAT"),
                 bigquery.SchemaField("int8_col", "INTEGER"),