Polish datetime conversion implementation

- Naming things
- Slight structural changes
- Use iterator instead of generator for column type flagging
- Improve inline documentation

Author: amotl

src/crate/client/cursor.py

@@ -51,44 +51,45 @@ def execute(self, sql, parameters=None, bulk_parameters=None):
         self._result = self.connection.client.sql(sql, parameters,
                                                   bulk_parameters)
 
-        if "rows" in self._result:
-            transformed_result = False
-            if "col_types" in self._result:
-                transformed_result = True
-                self.rows = self.result_set_transformed()
+        if "rows" not in self._result:
+            return
+
+        if "col_types" in self._result:
+            self.rows = iter(self._transform_result_types())
 
-            if not transformed_result:
-                self.rows = iter(self._result["rows"])
+        else:
+            self.rows = iter(self._result["rows"])
 
-    def result_set_transformed(self):
+    def _transform_result_types(self):
         """
-        Generator that iterates over each row from the result set
+        Generate row items with column values converted to their corresponding
+        native Python types, based on information from `col_types`.
+
+        Currently, only converting to native `datetime` objects is implemented.
         """
-        rows_to_convert = [True if col_type == 11 or col_type == 15 else False for col_type in
-                           self._result["col_types"]]
+        datetime_column_types = [11, 15]
+        datetime_columns_mask = [
+            True if col_type in datetime_column_types else False
+            for col_type in self._result["col_types"]
+        ]
         for row in self._result["rows"]:
-            gen_flags = (flag for flag in rows_to_convert)
-            yield [t_row for t_row in self._transform_date_columns(row, gen_flags)]
+            yield list(self._transform_datetime_columns(row, iter(datetime_columns_mask)))
 
     @staticmethod
-    def _transform_date_columns(row, gen_flags):
+    def _transform_datetime_columns(row, column_flags):
         """
-        Generates iterates over each value from a row and converts timestamps to pandas TIMESTAMP
+        Convert all designated columns to native Python `datetime` objects.
         """
         for value in row:
             try:
-                flag = next(gen_flags)
+                flag = next(column_flags)
             except StopIteration:
                 break
 
-            if not flag or value is None:
-                yield value
-            else:
-                if value < 0:
-                    yield None
-                else:
-                    value = datetime.fromtimestamp(value / 1000)
-                    yield value
+            if flag and value is not None:
+                value = datetime.fromtimestamp(value / 1e3)
+
+            yield value
 
     def executemany(self, sql, seq_of_parameters):
         """