Warn the user if they are trying to save an unfit synthesizer (#2147)

sdv/multi_table/base.py

@@ -665,13 +665,23 @@ def get_info(self):
 
         return info
 
+    def _validate_fit_before_save(self):
+        """Validate that the synthesizer has been fitted before saving."""
+        if not self._fitted:
+            warnings.warn(
+                'You are saving a synthesizer that has not yet been fitted. You will not be able '
+                'to sample synthetic data without fitting. We recommend fitting the synthesizer '
+                'first and then saving.'
+            )
+
     def save(self, filepath):
         """Save this instance to the given path using cloudpickle.
 
         Args:
             filepath (str):
                 Path where the instance will be serialized.
         """
+        self._validate_fit_before_save()
         synthesizer_id = getattr(self, '_synthesizer_id', None)
         SYNTHESIZER_LOGGER.info({
             'EVENT': 'Save',

sdv/single_table/base.py

@@ -471,13 +471,23 @@ def fit(self, data):
         processed_data = self.preprocess(data)
         self.fit_processed_data(processed_data)
 
+    def _validate_fit_before_save(self):
+        """Validate that the synthesizer has been fitted before saving."""
+        if not self._fitted:
+            warnings.warn(
+                'You are saving a synthesizer that has not yet been fitted. You will not be able '
+                'to sample synthetic data without fitting. We recommend fitting the synthesizer '
+                'first and then saving.'
+            )
+
     def save(self, filepath):
         """Save this model instance to the given path using cloudpickle.
 
         Args:
             filepath (str):
                 Path where the synthesizer instance will be serialized.
         """
+        self._validate_fit_before_save()
         synthesizer_id = getattr(self, '_synthesizer_id', None)
         SYNTHESIZER_LOGGER.info({
             'EVENT': 'Save',

tests/unit/multi_table/test_base.py

@@ -1,4 +1,5 @@
 import logging
+import os
 import re
 import warnings
 from collections import defaultdict
@@ -1521,6 +1522,21 @@ def test_save(self, cloudpickle_mock, mock_datetime, tmp_path, caplog):
             'SYNTHESIZER ID': 'BaseMultiTableSynthesizer_1.0.0_92aff11e9a5649d1a280990d1231a5f5',
         })
 
+    def test_save_warning(self, tmp_path):
+        """Test that the synthesizer produces a warning if saved without fitting."""
+        # Setup
+        synthesizer = BaseMultiTableSynthesizer(MultiTableMetadata())
+
+        # Run and Assert
+        warn_msg = re.escape(
+            'You are saving a synthesizer that has not yet been fitted. You will not be able '
+            'to sample synthetic data without fitting. We recommend fitting the synthesizer '
+            'first and then saving.'
+        )
+        with pytest.warns(Warning, match=warn_msg):
+            filepath = os.path.join(tmp_path, 'output.pkl')
+            synthesizer.save(filepath)
+
     @patch('sdv.multi_table.base.datetime')
     @patch('sdv.multi_table.base.generate_synthesizer_id')
     @patch('sdv.multi_table.base.check_synthesizer_version')

tests/unit/single_table/test_base.py

@@ -1,4 +1,5 @@
 import logging
+import os
 import re
 from datetime import date, datetime
 from unittest.mock import ANY, MagicMock, Mock, call, mock_open, patch
@@ -32,7 +33,7 @@
     GaussianCopulaSynthesizer,
     TVAESynthesizer,
 )
-from sdv.single_table.base import COND_IDX, BaseSingleTableSynthesizer
+from sdv.single_table.base import COND_IDX, BaseSingleTableSynthesizer, BaseSynthesizer
 from tests.utils import catch_sdv_logs
 
 
@@ -1809,6 +1810,21 @@ def test_save(self, cloudpickle_mock, mock_datetime, tmp_path, caplog):
             'SYNTHESIZER ID': 'BaseSingleTableSynthesizer_1.0.0_92aff11e9a5649d1a280990d1231a5f5',
         })
 
+    def test_save_warning(self, tmp_path):
+        """Test that the synthesizer produces a warning if saved without fitting."""
+        # Setup
+        synthesizer = BaseSynthesizer(SingleTableMetadata())
+
+        # Run and Assert
+        warn_msg = re.escape(
+            'You are saving a synthesizer that has not yet been fitted. You will not be able '
+            'to sample synthetic data without fitting. We recommend fitting the synthesizer '
+            'first and then saving.'
+        )
+        with pytest.warns(Warning, match=warn_msg):
+            filepath = os.path.join(tmp_path, 'output.pkl')
+            synthesizer.save(filepath)
+
     @patch('sdv.single_table.base.datetime')
     @patch('sdv.single_table.base.generate_synthesizer_id')
     @patch('sdv.single_table.base.check_synthesizer_version')