feat: add pythonic hub reader indexing

atompack-py/python/atompack/hub.py

@@ -171,9 +171,18 @@ def __len__(self) -> int:
         self._ensure_open()
         return self._total_length
 
-    def __getitem__(self, index: int) -> Molecule:
+    def __getitem__(self, index: int | slice) -> Molecule | list[Molecule]:
+        if isinstance(index, slice):
+            self._ensure_open()
+            start, stop, step = index.indices(self._total_length)
+            return self.get_molecules(list(range(start, stop, step)))
         return self.get_molecule(index)
 
+    def __iter__(self):
+        self._ensure_open()
+        for index in range(self._total_length):
+            yield self.get_molecule(index)
+
     def get_molecule(self, index: int) -> Molecule:
         db_index, local_index = self._locate(index)
         return self._databases[db_index][local_index]

atompack-py/python/atompack/hub.pyi

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from pathlib import Path
 from types import TracebackType
-from typing import Any, Sequence
+from typing import Any, Iterator, Sequence, overload
 
 from . import Molecule
 
@@ -26,6 +26,7 @@ class AtompackReader:
     def __len__(self) -> int:
         """Return the total number of molecules across all opened files."""
         ...
+    @overload
     def __getitem__(self, index: int) -> Molecule:
         """
         Fetch one molecule by index.
@@ -34,6 +35,8 @@ class AtompackReader:
         dataset, not within a single shard.
         """
         ...
+    @overload
+    def __getitem__(self, index: slice) -> list[Molecule]: ...
     def get_molecule(self, index: int) -> Molecule:
         """
         Fetch one molecule by global index across the underlying shard set.
@@ -75,6 +78,9 @@ class AtompackReader:
     def close(self) -> None:
         """Close the underlying databases and invalidate the reader."""
         ...
+    def __iter__(self) -> Iterator[Molecule]:
+        """Iterate over molecules in logical reader order."""
+        ...
 
 def download(
     repo_id: str,

atompack-py/tests/test_hub.py

@@ -415,6 +415,21 @@ def test_open_path_directory_flattens_lexicographically(tmp_path: Path) -> None:
     assert [reader[i].energy for i in range(len(reader))] == pytest.approx([-1.0, -2.0, -3.0])
 
 
+def test_reader_supports_iteration_and_slices(tmp_path: Path) -> None:
+    shard_dir = tmp_path / "shards"
+    shard_dir.mkdir()
+    _make_db(shard_dir / "a.atp", [-1.0, -2.0])
+    _make_db(shard_dir / "b.atp", [-3.0, -4.0])
+
+    reader = atompack.hub.open_path(shard_dir)
+
+    assert [molecule.energy for molecule in reader] == pytest.approx([-1.0, -2.0, -3.0, -4.0])
+    assert [molecule.energy for molecule in reader[1:4:2]] == pytest.approx([-2.0, -4.0])
+    assert [molecule.energy for molecule in reader[::-1]] == pytest.approx(
+        [-4.0, -3.0, -2.0, -1.0]
+    )
+
+
 def test_open_path_context_manager_closes_reader(tmp_path: Path) -> None:
     source = tmp_path / "single.atp"
     _make_db(source, [-1.0])

atompack-py/tests/test_stub_surface.py

@@ -76,6 +76,9 @@ def test_public_stub_exposes_flat_batch_reader() -> None:
 
 
 def test_hub_stub_has_public_docstrings() -> None:
+    reader_methods = _class_method_names(HUB_STUB, "AtompackReader")
+    assert {"__getitem__", "__iter__"} <= reader_methods
+
     reader_doc = _class_docstring(HUB_STUB, "AtompackReader") or ""
     assert "lexicographically ordered shard set" in reader_doc