The

state.json

file is used in the context of incremental sync in Airbyte's Python CDK. Incremental sync is a method of data replication in which only new or updated data is replicated, reducing the amount of data transferred and improving efficiency. In the Python CDK, the

state.json

file is used to store the state of the data sync. This state is represented by a

dict

object, which typically contains a single key-value pair. The key is

'date'

and the value is the date of the last day data was synced from. For example,

{'date': '2021-04-26'}

indicates that the connector previously read data up until April 26th and therefore shouldn't re-read anything before that date. The

state

attribute is managed by the

IncrementalMixin

class, which provides a getter and setter for the state. The getter serializes the internal state of the stream, while the setter deserializes the state saved by the CDK and initializes the internal state of the stream. Here's an example of how the

state

attribute is used in the

ExchangeRates

class:

python @property   def state(self) -> Mapping[str, Any]:    return {self.cursor_field: str(self._cursor_value)}      @state.setter   def state(self, value: Mapping[str, Any]):    self._cursor_value = value[self.cursor_field]

The

state.json

file is updated during the

read_records

method, right after the latest record returned that matches the new state. Therefore, the state represents the latest checkpoint successfully achieved, and all next records should match the next state after that one. You can save the latest state to

state.json

and run a read operation with the latest state message like this:

bash # Save the latest state to sample_files/state.json   python main.py read --config secrets/config.json --catalog sample_files/configured_catalog.json | grep STATE | tail -n 1 | jq .state.data > sample_files/state.json      # Run a read operation with the latest state message   python main.py read --config secrets/config.json --catalog sample_files/configured_catalog.json --state sample_files/state.json

For more information, you can refer to the [Airbyte documentation](https://docs.airbyte.com/connector-development/cdk-python/incremental-stream) and the [Python CDK tutorial](https://docs.airbyte.com/connector-development/tutorials/cdk-tutorial-python-http/read-data).