Problem with timestamp when they are not integer in python

Traceback (most recent call last):
  File "/home/arnaud/.local/lib/python3.10/site-packages/pytezos/michelson/micheline.py", line 38, in wrapper
    return func(*args, **kwargs)
  File "/home/arnaud/.local/lib/python3.10/site-packages/pytezos/michelson/types/domain.py", line 61, in to_micheline_value
    return {'string': format_timestamp(self.value)}
  File "/home/arnaud/.local/lib/python3.10/site-packages/pytezos/michelson/format.py", line 14, in format_timestamp
    dt = datetime.utcfromtimestamp(timestamp)
TypeError: ('timestamp', "'str' object cannot be interpreted as an integer")

When redeploying the smart contract of the factori documentation (KT1Fjiwsmo49yM7jch6KG4ETLFkatF3Qj8of), the storage must be generetated randomly because of the storage on the blockchain that has a timestamp field like that "2023-05-15T15:18:11Z"