Replaying Temporal Workflow from JSON in Python

Community Support
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1

I have a temporal workflow class that I am modifying over time, and I want to make sure that in-flight workflows are never broken.

I have downloaded the JSON history of a complete workflow, and am trying to construct the history from that workflow and then replay to ensure there are no errors. However, I’m running into the following problem using the python SDK:

My code:

with open(history_file, "r") as f:
    history_json = json.load(f)
# Replay the Workflow history
await replayer.replay_workflow(
    WorkflowHistory.from_json("dummy-id", history_json)
)

And the error I’m getting:

  File "/opt/venv/lib/python3.10/site-packages/temporalio/worker/_workflow_instance.py", line 2184, in start_activity
    return self._instance._outbound_schedule_activity(input)
  File "/opt/venv/lib/python3.10/site-packages/temporalio/worker/_workflow_instance.py", line 1458, in _outbound_schedule_activity
    handle._apply_schedule_command()
  File "/opt/venv/lib/python3.10/site-packages/temporalio/worker/_workflow_instance.py", line 2294, in _apply_schedule_command
    self._instance._payload_converter.to_payloads(self._input.args)
  File "/opt/venv/lib/python3.10/site-packages/temporalio/converter.py", line 269, in to_payloads
    payload = converter.to_payload(value)
  File "/opt/venv/lib/python3.10/site-packages/temporalio/converter.py", line 568, in to_payload
    data=json.dumps(
  File "/usr/local/lib/python3.10/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/usr/local/lib/python3.10/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/local/lib/python3.10/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/opt/venv/lib/python3.10/site-packages/temporalio/converter.py", line 512, in default
    return super().default(o)
  File "/usr/local/lib/python3.10/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
===============================================================================RuntimeError: 4: Workflow activation completion failed: Failure { failure: Some(Failure { message: "Object of type datetime is not JSON serializable", source: ""

I tried the following but it doesn’t work, and I get the same error:

def convert_datetime_to_string(obj):
    """Convert datetime objects to ISO 8601 string format."""
    if isinstance(obj, datetime):
        return obj.isoformat()
    raise TypeError(f"Type {type(obj)} not serializable")

with open(history_file, "r") as f:
    history_json = json.loads(json.dumps(json.load(f), default=convert_datetime_to_string))
# Replay the Workflow history
await replayer.replay_workflow(
    WorkflowHistory.from_json("dummy-id", history_json)
)
2

You are correct to use custom converter. Have seen users in past use simplejson to serialize datetime with success