Use safe ratio helper in regularity

src/lingrex/regularity.py

@@ -6,6 +6,7 @@
 from lingpy import log
 
 
+
 def regularity(wordlist, threshold=3, ref="cogid", min_refs=3,
                word_threshold=0.75, sound_classes="cv"):
     """
@@ -92,6 +93,20 @@ def regularity(wordlist, threshold=3, ref="cogid", min_refs=3,
             else:
                 irregular_words += len(set(msa["taxa"]))
 
+    if patterns == 0:
+        raise ValueError(
+            "Cannot compute regularity: no patterns were detected in the data. "
+            "Check sound_classes or input data."
+        )
+    if full_proportion == 0:
+        raise ValueError(
+            "Cannot compute regularity: no eligible alignment sites were found."
+        )
+    if (regular_words + irregular_words) == 0:
+        raise ValueError(
+            "Cannot compute regularity: no words satisfy the min_refs threshold."
+        )
+
     return (
         regular_patterns,
         patterns - regular_patterns,

tests/test_regularity.py

@@ -33,3 +33,17 @@ def test_regularity():
                         sound_classes="cv")
 
     assert output == (2, 5, 7, 0.29, 4, 5, 9, 0.44, 3, 4, 7, 0.43)
+    with raises(
+        ValueError,
+        match=r"Cannot compute regularity: no words satisfy the min_refs threshold\.",
+    ):
+        regularity(
+            test_alg, threshold=2, word_threshold=0.5, sound_classes="cv", min_refs=5
+        )
+    with raises(
+        ValueError,
+        match=r"Cannot compute regularity: no patterns were detected in the data\.",
+    ):
+        regularity(
+            test_alg, threshold=2, word_threshold=0.5, sound_classes="T"
+        )