convert sound to list of phonemes in python

I need to create the function audio_to_phonemes

You're basically saying:

I need to re-implement 40 years of speech recognition research

You shouldn't be implementing this yourself (unless you're about to be a professor in the field of speech recognition and have a revolutionary new approach), but should be using one of the many existing frameworks. Have a look at sphinx / pocketsphinx!

Accurate phoneme recognition is not easy to achieve because phonemes themselves are pretty loosely defined. Even in good audio the best possible systems today have about 18% phoneme error rate (you can check LSTM-RNN results on TIMIT published by Alex Graves).

In CMUSphinx phoneme recognition in Python is done like this:

from os import environ, path

from pocketsphinx.pocketsphinx import *
from sphinxbase.sphinxbase import *

MODELDIR = "../../../model"
DATADIR = "../../../test/data"

# Create a decoder with certain model
config = Decoder.default_config()
config.set_string('-hmm', path.join(MODELDIR, 'en-us/en-us'))
config.set_string('-allphone', path.join(MODELDIR, 'en-us/en-us-phone.lm.dmp'))
config.set_float('-lw', 2.0)
config.set_float('-beam', 1e-10)
config.set_float('-pbeam', 1e-10)

# Decode streaming data.
decoder = Decoder(config)

decoder.start_utt()
stream = open(path.join(DATADIR, 'goforward.raw'), 'rb')
while True:
  buf = stream.read(1024)
  if buf:
    decoder.process_raw(buf, False, False)
  else:
    break
decoder.end_utt()

hypothesis = decoder.hyp()
print ('Phonemes: ', [seg.word for seg in decoder.seg()])

You need to checkout latest pocketsphinx from github in order to run this example. Result should look like this:

  ('Best phonemes: ', ['SIL', 'G', 'OW', 'F', 'AO', 'R', 'W', 'ER', 'D', 'T', 'AE', 'N', 'NG', 'IY', 'IH', 'ZH', 'ER', 'Z', 'S', 'V', 'SIL'])

See also the wiki page