improve chain letter naming

chai_lab/chai1.py

@@ -86,7 +86,7 @@
 from chai_lab.data.features.generators.token_pair_pocket_restraint import (
     TokenPairPocketRestraint,
 )
-from chai_lab.data.io.cif_utils import save_to_cif
+from chai_lab.data.io.cif_utils import get_chain_letter, save_to_cif
 from chai_lab.data.parsing.restraints import parse_pairwise_table
 from chai_lab.data.parsing.structure.entity_type import EntityType
 from chai_lab.model.diffusion_schedules import InferenceNoiseSchedule
@@ -872,7 +872,7 @@ def avg_per_token_1d(x):
             inputs["atom_token_index"],
         )
 
-        ranking_outputs = rank(
+        ranking_outputs: SampleRanking = rank(
             atom_pos[idx : idx + 1],
             atom_mask=inputs["atom_exists_mask"],
             atom_token_index=inputs["atom_token_index"],
@@ -908,7 +908,8 @@ def avg_per_token_1d(x):
             write_path=cif_out_path,
             # Set asym names to be A, B, C, ...
             asym_entity_names={
-                i + 1: chr(i + 65) for i in range(len(feature_context.chains))
+                i: get_chain_letter(i)
+                for i in range(1, len(feature_context.chains) + 1)
             },
         )
         cif_paths.append(cif_out_path)

chai_lab/data/io/cif_utils.py

@@ -40,7 +40,9 @@ class _LocalPLDDT(modelcif.qa_metric.Local, modelcif.qa_metric.PLDDT):
 _CHAIN_VOCAB = _CHAIN_VOCAB + [x + y for x in _CHAIN_VOCAB for y in _CHAIN_VOCAB]
 
 
-def _get_chain_letter(asym_id: int) -> str:
+def get_chain_letter(asym_id: int) -> str:
+    """Get chain given a one-indexed asym_id."""
+    assert asym_id > 0 and asym_id <= len(_CHAIN_VOCAB)
     vocab_index = asym_id - 1  # 1 -> A, 2 -> B
     return _CHAIN_VOCAB[vocab_index]
 

tests/test_cif_utils.py

@@ -0,0 +1,24 @@
+# Copyright (c) 2024 Chai Discovery, Inc.
+# Licensed under the Apache License, Version 2.0.
+# See the LICENSE file for details.
+
+
+import pytest
+
+from chai_lab.data.io.cif_utils import get_chain_letter
+
+
+def test_get_chain_letter():
+    with pytest.raises(AssertionError):
+        get_chain_letter(0)
+    assert get_chain_letter(1) == "A"
+    assert get_chain_letter(26) == "Z"
+    assert get_chain_letter(27) == "a"
+    assert get_chain_letter(52) == "z"
+
+    assert get_chain_letter(53) == "AA"
+    assert get_chain_letter(54) == "AB"
+
+    # For one-letter codes, there are 26 + 26 = 52 codes
+    # For two-letter codes, there are 52 * 52 codes
+    assert get_chain_letter(52 * 52 + 52) == "zz"