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The PhoneticHasher converts Myanmar text into pronunciation-based hash codes, letting the suggestion engine surface candidates that sound alike, even when their spellings differ significantly.

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Phonetic Hasher

mySpellChecker includes a custom PhoneticHasher optimized for Myanmar phonology. It converts a string into a phonetic code, allowing for fuzzy matching based on pronunciation.

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Key Features

  • Consonant Grouping: Maps similar-sounding consonants (e.g., က vs ဂ) to the same code.
  • Tone Normalization: Can ignore tone marks (e.g., ကာ, ကား, က) to find tonal errors.
  • Vowel Normalization: Treats short and long vowels (e.g., ိ vs ီ) as identical.
  • Adaptive Length Encoding: Automatically extends the code length for compound words to preserve phonetic information.
  • Nasal Normalization: Optionally unifies various nasal endings (e.g., န်, မ်, င်) to the Anusvara (ံ) sound. Note: normalize_nasals defaults to False — you must explicitly enable it if needed.

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Python API

from myspellchecker.text.phonetic import PhoneticHasher

hasher = PhoneticHasher()

# 1. Encoding
code1 = hasher.encode("မြန်")  # -> 'p-medial_r-vowel_a-n'
code2 = hasher.encode("မျန်")  # -> 'p-medial_y-vowel_a-n' (Note difference)

# 2. Similarity Check
is_similar = hasher.similar(code1, code2, max_distance=1)
# True (Small edit distance in phonetic space)

# 3. Finding Variants
variants = hasher.get_phonetic_variants("မြန်")
# {'မြန်', 'မျန်', 'ဗြန်', ...}

# 4. Tonal Variants (for Real-Word Error detection)
tonal_vars = hasher.get_tonal_variants("ကား")
# {'ကား', 'ကာ', 'က'}

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How It Works

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Encoding Process

  1. Normalization: Text is converted to Unicode NFC form.
  2. Preprocessing: If normalize_nasals=True, common nasal endings (န်, မ်, င်) are normalized to ံ. (Disabled by default.)
  3. Mapping: Each character is mapped to a phonetic group code (e.g., KA_GROUP, MEDIAL_R).
  4. Filtering: Tone marks and viramas are optionally stripped.
  5. Concatenation: Codes are joined to form the final hash.

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Scoring

The compute_phonetic_similarity method uses a multi-factor scoring approach:
  1. Character-level similarity: Compares characters pairwise using Myanmar substitution costs (MYANMAR_SUBSTITUTION_COSTS), visual confusability, and phonetic group membership.
  2. Length penalty: Proportional penalty for length differences: (max_len - min_len) / max_len * 0.2.
  3. Phonetic code blending: Levenshtein distance on phonetic codes is blended with character-level similarity, with code weight scaled by input length (min(0.4, len / 20.0)).
Score = (1 - w) * CharSimilarity + w * CodeSimilarity - LengthPenalty Where CharSimilarity is the average per-character similarity using substitution costs, CodeSimilarity = 1 - Levenshtein(Code_A, Code_B) / MaxLen, and w = min(0.4, len(input) / 20.0).

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Usage in Spell Checking

Note: Phonetic hashing is computed at runtime, not stored in the database schema. There is no phonetic_hash column in the database tables. Hashes are generated on-the-fly using the PhoneticHasher during lookup.
  1. Lookup: When a word is unknown (OOV), the system computes its phonetic hash at runtime.
  2. Comparison: The hash is compared against hashes computed for dictionary candidates (from SymSpell delete index).
  3. Suggestion: Candidates are matched by:
    • Exact Hash Match: Words that sound identical.
    • Near Hash Match: Words that sound very similar (e.g., slight medial difference).

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Constructor Parameters

from myspellchecker.text.phonetic import PhoneticHasher

hasher = PhoneticHasher(
    ignore_tones=True,
    normalize_length=True,
    normalize_nasals=False,
    max_code_length=10,
    adaptive_length=True,
    chars_per_code_unit=6,
    cache_size=4096,
    config=None,  # Optional PhoneticConfig
)
ParameterTypeDefaultDescription
ignore_tonesboolTrueIgnore tone marks in encoding, making it more forgiving of tone mark errors.
normalize_lengthboolTrueTreat short/long vowels as the same (e.g., ိ and ီ produce the same code).
normalize_nasalsboolFalseNormalize nasal endings (န်, မ်, င်) to Anusvara (ံ). Increases recall but may cause false positives between /n/, /m/, and /ŋ/ sounds.
max_code_lengthint10Maximum length of phonetic codes. Base limit for simple words; may be extended for compounds when adaptive_length is enabled.
adaptive_lengthboolTrueAutomatically extend max_code_length for compound words to prevent information loss.
chars_per_code_unitint6Characters per phonetic code unit for adaptive length calculation (~6 input chars per code unit).
cache_sizeint4096Maximum size of the LRU encoding cache. Set to 0 to disable caching.
configPhoneticConfig | NoneNoneOptional PhoneticConfig for similarity scoring weights. When provided, encoding params (max_code_length, chars_per_code_unit, cache_size) are taken from config unless explicitly overridden.

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Configuration

Controlled by use_phonetic in SpellCheckerConfig.