Add type annotations to metadata mappings

Files in swh/indexer/metadata_dictionary/ currently do not have any type annotation. It would be nice to annotate all their functions.

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Migrated from T2259 (view on Phabricator)

mentioned in merge request !305 (closed)

marked this issue as related to #2257

added Easy hack Indexer priority:Low labels

hey, I would like to contribute.

Hi @vlorentz this will be my first contribution for Software Heritage so can you explain about the issue a little more. Also I am having some problems installing Arcanist (fatal error with php not getting resolved)into my system. Will it be possible to commit directly on github.

so can you explain about the issue a little more

The linked document should explain what type annotations are in Python; is there something you need help with?

Also I am having some problems installing Arcanist (fatal error with php not getting resolved)into my system.

Join the chat so we can try to help you

Will it be possible to commit directly on github.

No; we only have read-only mirrors on github, the actual development is here.

Thanks. Appreciate the help.

While annotating, are we expected to use native Python Datatypes (like str, int, float etc.) or do I use the NewType class of the Type library as in the example below:

from typing import NewType

UserId = NewType('UserId', int)
some_id = UserId(524313)

mentioned in merge request !295 (closed)