Fix TypeError in singular_noun for 'pair of scissors' (#222)

inflect/__init__.py

@@ -3007,8 +3007,14 @@ def _handle_long_compounds(self, word: Words, count: int) -> Union[str, None]:
         Handles the plural and singular for compound `Words` that
         have three or more words, based on the given count.
 
+        When the candidate word is already in the requested form,
+        ``self._sinoun`` / ``self._plnoun`` returns ``False``; fall back
+        to the original word so the joined phrase remains a string. (#222)
+
         >>> engine()._handle_long_compounds(Words("pair of scissors"), 2)
         'pairs of scissors'
+        >>> engine()._handle_long_compounds(Words("pair of scissors"), 1)
+        'pair of scissors'
         >>> engine()._handle_long_compounds(Words("men beyond hills"), 1)
         'man beyond hills'
         """
@@ -3017,7 +3023,7 @@ def _handle_long_compounds(self, word: Words, count: int) -> Union[str, None]:
             " ".join(
                 itertools.chain(
                     leader,
-                    [inflection(cand, count), prep],  # type: ignore[operator]
+                    [inflection(cand, count) or cand, prep],
                     trailer,
                 )
             )

newsfragments/222.bugfix.rst

@@ -0,0 +1,5 @@
+Fix ``TypeError`` raised by ``singular_noun`` for compound phrases ending
+in an uninflected word (e.g. ``"pair of scissors"``). When the candidate
+word is already singular, ``_sinoun`` returns ``False``; the long-compound
+handler now falls back to the original word so the joined phrase remains
+a string.

tests/test_compounds.py

@@ -19,6 +19,18 @@ def test_compound_4():
     assert p.singular_noun("case of diapers") == "case of diapers"
 
 
+def test_singular_noun_already_singular_long_compound():
+    """
+    Compound phrases routed through ``_handle_long_compounds`` whose
+    candidate word is already singular previously raised ``TypeError``
+    because ``_sinoun`` returned ``False`` and that fell into ``str.join``.
+    See https://github.com/jaraco/inflect/issues/222.
+    """
+    assert p.singular_noun("pair of scissors") == "pair of scissors"
+    # The pluralized form should still round-trip back to the singular.
+    assert p.singular_noun("pairs of scissors") == "pair of scissors"
+
+
 def test_unit_handling_degree():
     test_cases = {
         "degree celsius": "degrees celsius",