Downloading and caching checkpoints

[sidharthrajaram]

Downloading and caching ability when loading checkpoints (similar to Transformers API).

• Can now provide a checkpoint filename or a checkpoint URL (or just a file path as before). Regardless, value passed to checkpoint_path in Phonemizer.from_checkpoint() should end with .pt. See test results below.
• If just a checkpoint name is provided, it will try to retrieve the checkpoint under the DEFAULT_MODEL_BUCKET (see dp/model/model.py).
• Caching is facilitated with cached_path

Why?

• Convenient checkpoint loading (familiar behavior to what we're used to with Transformers/HuggingFace).
• No longer have to manage location of checkpoints.
• Enables easier model fetching (if your own trained checkpoints are on S3, MinIO, etc.)

Test cases:

Invalid file

>>> phonemizer = Phonemizer.from_checkpoint('test')
ValueError: test is not a valid model file (.pt).

Invalid checkpoint file

>>> phonemizer = Phonemizer.from_checkpoint('test.pt')
...
requests.exceptions.HTTPError: 403 Client Error: Forbidden for url: https://public-asai-dl-models.s3.eu-central-1.amazonaws.com/DeepPhonemizer/test.pt

Checkpoint name provided

>>> phonemizer = Phonemizer.from_checkpoint('en_us_cmudict_forward.pt')
Loading model from /PATH/TO/.cache/cached_path/6c84425c...
>>>

Cached model loaded

>>> phonemizer = Phonemizer.from_checkpoint('en_us_cmudict_forward.pt')
Loading model from /PATH/TO/.cache/cached_path/6c84425c...
>>>

URL to checkpoint provided

>>> phonemizer = Phonemizer.from_checkpoint('https://public-asai-dl-models.s3.eu-central-1.amazonaws.com/DeepPhonemizer/en_us_cmudict_ipa_forward.pt')
Loading model from /PATH/TO/.cache/cached_path/3f662135...
>>>

Cached model loaded (with just checkpoint name)

>>> phonemizer = Phonemizer.from_checkpoint('en_us_cmudict_ipa_forward.pt')
en_us_cmudict_ipa_forward.pt already exists in cache.
Loading model from /PATH/TO/.cache/cached_path/3f662135...
>>>

Cached model loaded (with checkpoint URL)

>>> phonemizer = Phonemizer.from_checkpoint('https://public-asai-dl-models.s3.eu-central-1.amazonaws.com/DeepPhonemizer/en_us_cmudict_ipa_forward.pt')
en_us_cmudict_ipa_forward.pt already exists in cache.
Loading model from /PATH/TO/.cache/cached_path/3f662135...
>>>