Support empty compressed list objects of size n

Author: jkanche

CHANGELOG.md

@@ -1,9 +1,10 @@
 # Changelog
 
-## Version 0.4.0
+## Version 0.4.0 - 0.4.1
 
 - Classes extend `BiocObject` from biocutils. `metadata` is a named list.
 - Update actions to run from 3.10-3.14
+- Support empty compressed list objects of size `n`.
 
 ## Version 0.3.0
 

src/compressed_lists/base.py

@@ -387,11 +387,14 @@ def __getitem__(self, key: Union[int, str, slice]) -> Any:
 
             current_class_const = type(self)
             return current_class_const.from_list(
-                result, names=[self.names[i] for i in indices] if self.names[0] is not None else None
+                result, names=[self.names[i] for i in indices] if self.names is not None else None
             )
 
         else:
-            raise TypeError("'key' must be int, str, or slice.")
+            try:
+                return self.extract_subset(indices=key)
+            except Exception as e:
+                raise TypeError("'key' must be int, str, slice or list of indices.") from e
 
     ##################################
     ######>> abstract methods <<######
@@ -575,3 +578,19 @@ def lapply(self, func: Callable) -> CompressedList:
 
         current_class_const = type(self)
         return current_class_const.from_list(result, self.names, self._metadata)
+
+    @classmethod
+    def empty(cls, n: int):
+        """Create an zero-length `CompressedGenomicRangesList` object.
+
+        Args:
+            n:
+                Number of elements.
+
+        Returns:
+            same type as caller, in this case a `CompressedGenomicRangesList`.
+        """
+
+        _range_lengths = [0] * n
+
+        return CompressedList(unlist_data=[], partitioning=Partitioning(ends=_range_lengths))

tests/test_base.py

@@ -39,6 +39,19 @@ def test_base_list_of_empty():
     assert list(cl_list_empty[2]) == []
 
 
+def test_base_list_empty_classmeth():
+    cl_list_empty = CompressedList.empty(n=3)
+    assert len(cl_list_empty) == 3
+    assert len(cl_list_empty.unlist_data) == 0
+    assert list(cl_list_empty.get_element_lengths()) == [0, 0, 0]
+    assert list(cl_list_empty[0]) == []
+    assert list(cl_list_empty[1]) == []
+    assert list(cl_list_empty[2]) == []
+
+    subset = cl_list_empty[[0, 2]]
+    assert isinstance(subset, CompressedList)
+    assert len(subset) == 2
+
 def test_base_set_names(base_list):
     new_names = ["X", "Y", "Z"]