Fix tone_detector and sound_syllable bugs for Thai syllables (fixes #1055 and #1176)

pythainlp/util/syllable.py

@@ -95,6 +95,17 @@ def sound_syllable(syllable: str) -> str:
     ):
         return "live"
 
+    # Handle syllables with only อ (no other consonants from thai_consonants_all)
+    if len(consonants) == 0 and "อ" in syllable:
+        # Syllables with only อ and long vowels are live
+        if any((c in set("าีืแูเโไใำ")) for c in syllable):
+            return "live"
+        # Short vowels or special cases
+        if any((c in set(short)) for c in syllable):
+            return "dead"
+        # Default to live for vowel-only syllables
+        return "live"
+
     # get spelling consonants
     spelling_consonant = consonants[-1]
     if (spelling_consonant in _check_2) and (
@@ -228,6 +239,10 @@ def _check_sonorant_syllable(syllable: str) -> bool:
     _sonorant = [i for i in syllable if i in thai_low_sonorants]
     consonants = [i for i in syllable if i in list(thai_consonants)]
 
+    # Return False if no sonorants or not enough consonants
+    if not _sonorant or len(consonants) < 2:
+        return False
+
     if _sonorant[-1] == consonants[-2]:
         return True
 
@@ -267,87 +282,104 @@ def tone_detector(syllable: str) -> str:
     s = sound_syllable(syllable)
     # get consonants
     consonants = [i for i in syllable if i in list(thai_consonants)]
+
+    # Handle syllables with no consonants (e.g., ฤ, ฦ)
+    if len(consonants) == 0:
+        return ""
+
     initial_consonant = consonants[0]
     tone_mark = _tone_mark_detector(syllable)
     syllable_check = syllable_open_close_detector(syllable)
     syllable_check_length = syllable_length(syllable)
     initial_consonant_type = thai_initial_consonant_to_type[initial_consonant]
     # r for store value
     r = ""
+    # Special handling for อ and ห with sonorants
     if len(consonants) > 1 and (initial_consonant in ("อ", "ห")):
         consonant_ending = _check_sonorant_syllable(syllable)
-        if (
-            initial_consonant == "อ"
-            and consonant_ending
-            and s == "live"
-            and tone_mark == "่"
-        ):
-            r = "l"
-        elif (
-            initial_consonant == "ห"
-            and consonant_ending
-            and s == "live"
-            and tone_mark == "่"
-        ):
-            r = "l"
-        elif initial_consonant == "อ" and consonant_ending and s == "dead":
-            r = "l"
-        elif (
-            initial_consonant == "ห"
-            and consonant_ending
-            and s == "live"
-            and tone_mark == "้"
-        ):
-            r = "f"
-        elif initial_consonant == "ห" and consonant_ending and s == "dead":
-            r = "l"
-        elif initial_consonant == "ห" and consonant_ending and s == "live":
-            r = "r"
-    elif initial_consonant_type == "high" and s == "live" and tone_mark == "่":
+        if consonant_ending:
+            # Only apply special rules if there are sonorants
+            if (
+                initial_consonant == "อ"
+                and s == "live"
+                and tone_mark == "่"
+            ):
+                r = "l"
+            elif (
+                initial_consonant == "ห"
+                and s == "live"
+                and tone_mark == "่"
+            ):
+                r = "l"
+            elif initial_consonant == "อ" and s == "dead":
+                r = "l"
+            elif (
+                initial_consonant == "ห"
+                and s == "live"
+                and tone_mark == "้"
+            ):
+                r = "f"
+            elif initial_consonant == "ห" and s == "dead":
+                r = "l"
+            elif initial_consonant == "ห" and s == "live":
+                r = "r"
+    # If r is still empty, apply general tone rules
+    if r == "" and initial_consonant_type == "high" and s == "live" and tone_mark == "่":
         r = "l"
-    elif initial_consonant_type == "mid" and s == "live" and tone_mark == "่":
+    if r == "" and initial_consonant_type == "mid" and s == "live" and tone_mark == "่":
         r = "l"
-    elif initial_consonant_type == "low" and tone_mark == "้":
+    if r == "" and initial_consonant_type == "low" and tone_mark == "้":
         r = "h"
-    elif initial_consonant_type == "mid" and tone_mark == "๋":
+    if r == "" and initial_consonant_type == "mid" and tone_mark == "๋":
         r = "r"
-    elif initial_consonant_type == "mid" and tone_mark == "๊":
+    if r == "" and initial_consonant_type == "mid" and tone_mark == "๊":
         r = "h"
-    elif initial_consonant_type == "low" and tone_mark == "่":
+    if r == "" and initial_consonant_type == "low" and tone_mark == "่":
         r = "f"
-    elif initial_consonant_type == "mid" and tone_mark == "้":
+    if r == "" and initial_consonant_type == "mid" and tone_mark == "้":
         r = "f"
-    elif initial_consonant_type == "high" and tone_mark == "้":
+    if r == "" and initial_consonant_type == "high" and tone_mark == "้":
         r = "f"
-    elif (
-        initial_consonant_type == "low"
+    if (
+        r == ""
+        and initial_consonant_type == "low"
         and syllable_check_length == "short"
         and syllable_check == "close"
         and s == "dead"
     ):
         r = "h"
-    elif (
-        initial_consonant_type == "low"
+    if (
+        r == ""
+        and initial_consonant_type == "low"
         and syllable_check_length == "long"
         and syllable_check == "close"
         and s == "dead"
     ):
         r = "f"
-    elif (
-        initial_consonant_type == "low"
+    if (
+        r == ""
+        and initial_consonant_type == "low"
         and syllable_check_length == "short"
         and syllable_check == "open"
     ):
         r = "h"
-    elif initial_consonant_type == "mid" and s == "dead":
+    if (
+        r == ""
+        and initial_consonant_type == "low"
+        and syllable_check_length == "long"
+        and syllable_check == "open"
+        and s == "dead"
+    ):
+        r = "f"
+    if r == "" and initial_consonant_type == "mid" and s == "dead":
         r = "l"
-    elif initial_consonant_type == "high" and s == "dead":
+    if r == "" and initial_consonant_type == "high" and s == "dead":
         r = "l"
-    elif initial_consonant_type == "low" and s == "live":
+    if r == "" and initial_consonant_type == "low" and s == "live":
         r = "m"
-    elif initial_consonant_type == "mid" and s == "live":
+    if r == "" and initial_consonant_type == "mid" and s == "live":
         r = "m"
-    elif initial_consonant_type == "high" and s == "live":
+    if r == "" and initial_consonant_type == "high" and s == "live":
         r = "r"
 
     return r

tests/core/test_util.py

@@ -725,6 +725,58 @@ def test_tone_detector(self):
             ("h", "ครับ"),
             ("f", "ค่ะ"),
             ("m", "เอ"),
+            # Test cases from issue #1176 - syllables that previously returned UNKNOWN_tone
+            # Low consonant + dead + long + open → falling tone
+            ("f", "คอ"),
+            ("f", "พฤ"),
+            ("f", "พอ"),
+            ("f", "หญ้า"),
+            ("f", "อ้อม"),
+            ("f", "อ้าง"),
+            ("f", "เท"),
+            ("f", "เธอ"),
+            ("f", "เพ"),
+            ("f", "เภอ"),
+            ("f", "เอื้อ"),
+            ("f", "แฟ"),
+            ("f", "โค"),
+            ("f", "โฆ"),
+            ("f", "ไอ้"),
+            # Mid/high consonant + dead → low tone
+            ("l", "หรอก"),
+            ("l", "หลอก"),
+            ("l", "หัก"),
+            ("l", "หาก"),
+            ("l", "ห่อ"),
+            ("l", "อด"),
+            ("l", "อดีต"),
+            ("l", "อธิ"),
+            ("l", "อบ"),
+            ("l", "ออก"),
+            ("l", "อะ"),
+            ("l", "อัด"),
+            ("l", "อาจ"),
+            ("l", "อาด"),
+            ("l", "อิ"),
+            ("l", "อีก"),
+            ("l", "อุต"),
+            ("l", "อุป"),
+            ("l", "อู่"),
+            ("l", "เหตุ"),
+            ("l", "เอก"),
+            ("l", "แอบ"),
+            ("l", "ใหญ่"),
+            # Mid consonant + live → mid tone (especially syllables with only อ)
+            ("m", "อนา"),
+            ("m", "อัตรา"),
+            ("m", "อา"),
+            ("m", "อำ"),
+            ("m", "เอง"),
+            ("m", "เอา"),
+            ("m", "แอ"),
+            ("m", "โอ"),
+            ("m", "โอน"),
+            ("m", "ไอ"),
         ]
         for i, j in data:
             self.assertEqual(