Add try_get_chapters to scripture parsing

machine/scripture/__init__.py

@@ -20,7 +20,7 @@
     SEPTUAGINT_VERSIFICATION,
     VULGATE_VERSIFICATION,
 )
-from .parse import get_books, get_chapters
+from .parse import get_books, get_chapters, try_get_chapters
 from .verse_ref import (
     NULL_VERSIFICATION,
     VERSE_RANGE_SEPARATOR,
@@ -44,6 +44,7 @@
     "get_bbbcccvvv",
     "get_books",
     "get_chapters",
+    "try_get_chapters",
     "is_book_id_valid",
     "is_canonical",
     "is_nt",

machine/scripture/parse.py

@@ -1,5 +1,5 @@
 import re
-from typing import Dict, List, Set, Union
+from typing import Dict, List, Optional, Set, Union
 
 from .canon import book_id_to_number, book_number_to_id
 from .constants import ORIGINAL_VERSIFICATION
@@ -57,6 +57,8 @@ def _update_selection(book_set: Set[int], book_nums: Set[int], subtraction: bool
 
 def parse_selection(selection: str, versification: Versification) -> Dict[int, List[int]]:
     selection = selection.strip()
+    if len(selection) == 0:
+        raise ValueError("Empty book range.")
     chapters = {}
 
     if selection[-1].isdigit() and len(selection) > 3:  # Specific chapters from one book
@@ -179,3 +181,12 @@ def get_chapters(
                     chapters[book] = selection_chapters[book]
 
     return chapters
+
+
+def try_get_chapters(
+    selections: Union[str, List[str]], versification: Versification = ORIGINAL_VERSIFICATION
+) -> Optional[Dict[int, List[int]]]:
+    try:
+        return get_chapters(selections, versification)
+    except ValueError:
+        return None

tests/scripture/test_parse.py

@@ -1,6 +1,6 @@
 from pytest import raises
 
-from machine.scripture import get_books, get_chapters
+from machine.scripture import get_books, get_chapters, try_get_chapters
 
 
 def test_get_books() -> None:
@@ -177,3 +177,30 @@ def test_get_chapters() -> None:
         get_chapters("OT,MAT1")
     with raises(ValueError):
         get_chapters("OT,MAT-LUK")
+
+    # empty segments
+    with raises(ValueError):
+        get_chapters("MAT;;MRK")
+    with raises(ValueError):
+        get_chapters("  ;  ")
+    with raises(ValueError):
+        get_chapters(";")
+
+
+def test_try_get_chapters() -> None:
+    assert try_get_chapters("MAT1-4,12,9") == {40: [1, 2, 3, 4, 9, 12]}
+    assert try_get_chapters("") == {}
+    assert try_get_chapters(["MAT", "-MAT 1"]) == {40: list(range(2, 29))}
+
+    # invalid syntax, book, chapter, and subtraction
+    assert try_get_chapters("OT,MAT1") is None
+    assert try_get_chapters("ABC") is None
+    assert try_get_chapters("MAT 500") is None
+    assert try_get_chapters("MAT3-1") is None
+    assert try_get_chapters("-MRK") is None
+    assert try_get_chapters("MRK 2-5;-MRK 6") is None
+
+    # empty segments
+    assert try_get_chapters("MAT;;MRK") is None
+    assert try_get_chapters("  ;  ") is None
+    assert try_get_chapters(";") is None