[DEV] Deprecate specifying Vocab padding, bos and eos_token as positional arguments

[leezu]

Description

Deprecate specification as positional arguments in preparation for dropping explicit padding_token, bos_token and eos_token arguments in favor of the general kwargs handling of #732.

nlp.Vocab({'a':10}, None, 1, '<unk>', 'PAD')  # deprecated and will be unsupported
nlp.Vocab({'a':10}, None, 1, '<unk>', padding_token='PAD')  # recommended use

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Deprecate specifying Vocab padding, bos and eos_token as positional arguments

Comments

• We need to consider if we want to deprecate the current default values of padding, bos and eos_token as well in the future. Ie. if Vocab(counter) should still create Vocab(size=5, unk="<unk>", reserved="['<pad>', '<bos>', '<eos>']") or maybe Vocab(size=2, unk="<unk>", reserved="[]") The advantage is that there is nothing special about these 3 special tokens compared to other application specific special tokens; removing the default values simplifies our API. The disadvantage is that such change would affect the vast majority of users and most lines of code that instantiates Vocab. (Note, this is not part of this PR).

cc @dmlc/gluon-nlp-team

[codecov]

Codecov Report

Merging #945 into master will decrease coverage by 0.02%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master     #945      +/-   ##
==========================================
- Coverage   89.83%   89.81%   -0.03%     
==========================================
  Files          67       67              
  Lines        6364     6371       +7     
==========================================
+ Hits         5717     5722       +5     
- Misses        647      649       +2

Impacted Files	Coverage Δ
src/gluonnlp/vocab/vocab.py	96.39% <80%> (-0.94%)	⬇️

[szha]

PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)

[mli]

Job PR-945/8 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-945/8/index.html

[mli]

Job PR-945/10 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-945/10/index.html

[mli]

Job PR-945/11 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-945/11/index.html