class_docstr: Max. phonological unit, contains phones and triggers alternations.
class_docstr_tok: ["Max",".","phonological","unit",",","contains","phones","and","triggers","alternations","."]
docstr: Lengthen vowel before ns or nf.
docstr_tok: ["Lengthen","vowel","before","ns","or","nf","."]
code: def _ns_nf_lengthening(self):
      """
      Lengthen vowel before ns or nf.
      """
      out_phones = self.phones
      for n in range(len(self.phones)):
          p = self.phones[n]
          if (
              p.left.vow
              and "ː" not in p.left.ipa
              and p.ipa == "n̪"
              and (p.right.ipa == "s" or p.right.ipa == "f")
          ):
              out_phones[n - 1] = Phone(p.left.ipa + "ː")
      self.phones = out_phones
      self._refresh()
  
imports: import re
  import unicodedata
  from typing import List
  from nltk.tokenize import wordpunct_tokenize
  from cltk.core.cltk_logger import logger
  from cltk.prosody.lat import macronizer
label_desc: Use image node_id 11 for calling the Word obj's underlying member method code with example usage: obj._ns_nf_lengthening() without return types