fix(write): match DataFrame timestamp column by exact name

CHANGELOG.md

@@ -15,6 +15,7 @@
 1. [#723](https://github.com/influxdata/influxdb-client-python/pull/723): Export public names using generated `__all__` array in `__init__.py` as per reference documentation.
 1. [#725](https://github.com/influxdata/influxdb-client-python/pull/725): Start the `WritesRetry` `max_retry_time` at a request's first failure, so a strategy passed as `retries` to `InfluxDBClient` keeps retrying after `max_retry_time` has passed since it was created.
 1. [#732](https://github.com/influxdata/influxdb-client-python/pull/732): Apply the `#default` annotation in `FluxCsvParser` when it comes before `#datatype`.
+1. [#734](https://github.com/influxdata/influxdb-client-python/pull/734): Match `data_frame_timestamp_column` by exact column name, so a field whose name is part of the timestamp column name (e.g. `Open` with `OpenTime`) is no longer dropped.
 
 ## 1.50.0 [2026-01-23]
 

influxdb_client/client/write/dataframe_serializer.py

@@ -174,7 +174,7 @@ def __init__(self, data_frame, point_settings, precision=DEFAULT_WRITE_PRECISION
                     key_value = f',{key_format}={{str({val_format}).translate(_ESCAPE_KEY)}}'
                 tags.append(key_value)
                 continue
-            elif timestamp_column is not None and key in timestamp_column:
+            elif timestamp_column is not None and key == timestamp_column:
                 timestamp_index = field_index
                 continue
 

tests/test_WriteApiDataFrame.py

@@ -459,6 +459,23 @@ def test_use_timestamp_from_specified_column(self):
         self.assertEqual('test value1=10i,value2=30i 1586044800000000000', points[0])
         self.assertEqual('test value1=20i,value2=40i 1588636800000000000', points[1])
 
+    def test_timestamp_column_name_contains_field_name(self):
+        from influxdb_client.extras import pd
+        data_frame = pd.DataFrame(data={
+            'OpenTime': ['2020-04-05', '2020-05-05'],
+            'Open': [10, 20],
+            'Time': [30, 40],
+        }, index=['A', 'B'])
+
+        points = data_frame_to_list_of_points(data_frame=data_frame,
+                                              data_frame_measurement_name="test",
+                                              data_frame_timestamp_column="OpenTime",
+                                              point_settings=PointSettings())
+
+        self.assertEqual(2, len(points))
+        self.assertEqual('test Open=10i,Time=30i 1586044800000000000', points[0])
+        self.assertEqual('test Open=20i,Time=40i 1588636800000000000', points[1])
+
     def test_str_format_for_timestamp(self):
         from influxdb_client.extras import pd