Add better verification of source df data

pysdds/readers/readers.py

@@ -266,7 +266,7 @@ def read(filepath: Union[Path, str, IO[bytes]],
         pages_mask = None
 
     sdds = SDDSFile()
-    sdds.__source_file = str(filepath)
+    sdds._source_file = str(filepath)
 
     logger.debug(f'Opening file "%s"', str(filepath))
     #logger.debug(f'Mode (%s), compression (%s), endianness (%s)', mode, compression, endianness)

pysdds/structures/structures.py

@@ -969,13 +969,17 @@ def from_df(df_list: List[pd.DataFrame],
             else:
                 val = df.iloc[:, i].values
             sdds_type = constants._NUMPY_DTYPES_INV[df.dtypes.iloc[i]]
+            if sdds_type == object:
+                if not isinstance(val[0], str):
+                    raise ValueError(f'Column [{c}] is of object type but items are not strings')
             namelist = {'name': c, 'type': sdds_type}
             col = Column(namelist, sdds)
             sdds.columns.append(col)
             col.data.append(val)
 
         if parameter_dict is not None:
             for i, (k, v) in enumerate(parameter_dict.items()):
+                assert isinstance(v, list), f'Data of parameter [{k}] is not a list'
                 assert len(v) == n_pages, f'Length {len(v)} of parameter {k} different from page ' \
                                           f'count {n_pages}'
                 namelist = {'name': k, 'type': constants._PYTHON_TYPE_INV[type(v[0])]}