Improve error message when trying to sample before fitting (single table)

sdv/single_table/base.py

@@ -23,7 +23,8 @@
     _groupby_list, check_sdv_versions_and_warn, check_synthesizer_version, generate_synthesizer_id)
 from sdv.constraints.errors import AggregateConstraintsError
 from sdv.data_processing.data_processor import DataProcessor
-from sdv.errors import ConstraintsNotMetError, InvalidDataError, SynthesizerInputError
+from sdv.errors import (
+    ConstraintsNotMetError, InvalidDataError, SamplingError, SynthesizerInputError)
 from sdv.logging.utils import get_sdv_logger
 from sdv.single_table.utils import check_num_rows, handle_sampling_error, validate_file_path
 
@@ -871,6 +872,12 @@ def sample(self, num_rows, max_tries_per_batch=100, batch_size=None, output_file
             pandas.DataFrame:
                 Sampled data.
         """
+        if not self._fitted:
+            raise SamplingError(
+                'This synthesizer has not been fitted. Please fit your synthesizer first before'
+                ' sampling synthetic data.'
+            )
+
         sample_timestamp = datetime.datetime.now()
         has_constraints = bool(self._data_processor._constraints)
         has_batches = batch_size is not None and batch_size != num_rows

tests/integration/single_table/test_base.py

@@ -13,7 +13,7 @@
 
 from sdv import version
 from sdv.datasets.demo import download_demo
-from sdv.errors import SynthesizerInputError, VersionError
+from sdv.errors import SamplingError, SynthesizerInputError, VersionError
 from sdv.metadata import SingleTableMetadata
 from sdv.sampling import Condition
 from sdv.single_table import (
@@ -855,3 +855,19 @@ def test_synthesizer_logger(mock_datetime, mock_generate_id):
         '    Total number of columns: 3\n'
         '  Synthesizer id: GaussianCopulaSynthesizer_1.0.0_92aff11e9a5649d1a280990d1231a5f5\n'
     )
+
+
+@pytest.mark.parametrize('synthesizer', SYNTHESIZERS)
+def test_sample_not_fitted(synthesizer):
+    """Test that a synthesizer raises an error when trying to sample without fitting."""
+    # Setup
+    metadata = SingleTableMetadata()
+    synthesizer = synthesizer.__class__(metadata)
+    expected_message = re.escape(
+        'This synthesizer has not been fitted. Please fit your synthesizer first before'
+        ' sampling synthetic data.'
+    )
+
+    # Run and Assert
+    with pytest.raises(SamplingError, match=expected_message):
+        synthesizer.sample(10)

tests/unit/single_table/test_base.py

@@ -12,7 +12,7 @@
 
 from sdv import version
 from sdv.constraints.errors import AggregateConstraintsError
-from sdv.errors import ConstraintsNotMetError, SynthesizerInputError, VersionError
+from sdv.errors import ConstraintsNotMetError, SamplingError, SynthesizerInputError, VersionError
 from sdv.metadata.single_table import SingleTableMetadata
 from sdv.sampling.tabular import Condition
 from sdv.single_table import (
@@ -1399,6 +1399,20 @@ def test__sample_with_progress_bar_removing_temp_file(
         mock_os.remove.assert_called_once_with('.sample.csv.temp')
         mock_os.path.exists.assert_called_once_with('.sample.csv.temp')
 
+    def test_sample_not_fitted(self):
+        """Test that ``sample`` raises an error when the synthesizer is not fitted."""
+        # Setup
+        instance = Mock()
+        instance._fitted = False
+        expected_message = re.escape(
+            'This synthesizer has not been fitted. Please fit your synthesizer first before'
+            ' sampling synthetic data.'
+        )
+
+        # Run and Assert
+        with pytest.raises(SamplingError, match=expected_message):
+            BaseSingleTableSynthesizer.sample(instance, 10)
+
     @patch('sdv.single_table.base.datetime')
     def test_sample(self, mock_datetime, caplog):
         """Test that we use ``_sample_with_progress_bar`` in this method."""