fix(synthesizer): add already_fitted for synthesizer (#87)

src/ydata/sdk/synthesizers/synthesizer.py

@@ -100,7 +100,7 @@ def fit(self, X: Union[DataSource, pdDataFrame],
             anonymize (Optional[str]): (optional) fields to anonymize and the anonymization strategy
             condition_on: (Optional[List[str]]): (optional) list of features to condition upon
         """
-        if self._is_initialized():
+        if self._already_fitted():
             raise AlreadyFittedError()
 
         _datatype = DataSourceType(datatype) if isinstance(
@@ -383,6 +383,16 @@ def _is_initialized(self) -> bool:
         """
         return self._model is not None
 
+    def _already_fitted(self) -> bool:
+        """Determine if a synthesizer is already fitted.
+
+        Returns:
+            True if the synthesizer is instanciated
+        """
+
+        return self._is_initialized() and (self._model.status and self._model.status.training and
+                                           self._model.status.training.state is not [TrainingState.PREPARING])
+
     @staticmethod
     def _resolve_api_status(api_status: Dict) -> Status:
         """Determine the status of the Synthesizer.