Make DatabaseIterator abstract class

audb/core/stream.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import abc
 import os
 import typing
 
@@ -22,7 +23,7 @@
 from audb.core.lock import FolderLock
 
 
-class DatabaseIterator(audformat.Database):
+class DatabaseIterator(audformat.Database, metaclass=abc.ABCMeta):
     r"""Database iterator.
 
     This class cannot be created directly,
@@ -187,6 +188,21 @@ def __next__(self) -> pd.DataFrame:
 
         return df
 
+    @abc.abstractmethod
+    def _initialize_stream(self) -> typing.Iterable:
+        r"""Create table iterator object.
+
+        This method needs to be implemented
+        for the table file types
+        in the classes,
+        that inherit from :class:`audb.DatabaseIterator`.
+
+        Returns:
+            table iterator
+
+        """
+        return  # pragma: nocover
+
     @staticmethod
     def _cleanup_database(db: audformat.Database, table: str):
         r"""Remove parts of database, not used by table.
@@ -261,20 +277,6 @@ def _get_batch(self) -> pd.DataFrame:
 
         return df
 
-    def _initialize_stream(self) -> typing.Iterable:
-        r"""Create table iterator object.
-
-        This method needs to be implemented
-        for the table file types
-        in the classes,
-        that inherit from :class:`audb.DatabaseIterator`.
-
-        Returns:
-            table iterator
-
-        """
-        return None  # pragma: nocover
-
     def _load_media(self, df: pd.DataFrame):
         r"""Load media file for batch.
 

tests/test_stream.py

@@ -419,3 +419,34 @@ def test_errors(self, table: str, error, error_msg: str):
                 version=self.version,
                 verbose=False,
             )
+
+
+def test_database_iterator_error():
+    db = audformat.Database("db")
+    db["some"] = audformat.Table()
+    table = "some"
+    error_msg = (
+        "Can't instantiate abstract class DatabaseIterator "
+        "with abstract method _initialize_stream"
+    )
+    with pytest.raises(TypeError, match=error_msg):
+        audb.DatabaseIterator(
+            db,
+            table,
+            version=None,
+            map=None,
+            batch_size=16,
+            shuffle=False,
+            buffer_size=100_000,
+            only_metadata=False,
+            bit_depth=None,
+            channels=None,
+            format=None,
+            mixdown=False,
+            sampling_rate=None,
+            full_path=False,
+            cache_root=None,
+            num_workers=1,
+            timeout=-1,
+            verbose=False,
+        )