chore(mobilityd): Fix type errors shown by mypy

[sebathomas]

Summary

I tried static type checking of mobilityd using mypy and fixed some of the errors it found. Mostly these were minor issues (missing return statements or null checks).

The only bigger change is the introduction of dedicated types for IP addresses and networks. Before this PR, they referred to functions as variable types, which is not a valid type hint.

Test Plan

Install mypy in a virtualenv and execute it via

cd $MAGMA_ROOT/lte/gateway
mypy --ignore-missing-imports python/magma/mobilityd/

Error count on master:

Found 108 errors in 16 files (checked 31 source files)

Error count after the changes:

Found 24 errors in 5 files (checked 31 source files)

Additional Information

• This change is backwards-breaking

[github-actions]

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♻️ Updated: ✅ The check is passing the DCO check after the last commit.

[github-actions]

feg-workflow

    2 files  202 suites   33s ⏱️
363 tests 363 ✔️ 0 💤 0 ❌
377 runs  377 ✔️ 0 💤 0 ❌

Results for commit df4e3e9.

♻️ This comment has been updated with latest results.

[github-actions]

agw-workflow

  54 files    84 suites   3m 38s ⏱️
738 tests 729 ✔️ 9 💤 0 ❌
923 runs  914 ✔️ 9 💤 0 ❌

Results for commit df4e3e9.

[ardzoht]

lgtm

[themarwhal]

Thanks for this Sebastian!!! Is there a way to add linters / test coverage for these types of things?

[github-actions]

Unit Test Results

157 files  157 suites   2h 10m 43s ⏱️
307 tests 303 ✔️ 3 💤 1 ❌

For more details on these failures, see this check.

Results for commit 32ac5a3.

♻️ This comment has been updated with latest results.

[sebathomas]

Thanks for this Sebastian!!! Is there a way to add linters / test coverage for these types of things?

I'd love to have it in the CI. It would be easy to set up if we could fix all warnings first and then keep it green. Getting to a green state might take a lot of work though.

I'm not sure if there is any support for a mode with existing issues, e.g. where it checks that the number of errors doesn't increase so you could lower the allowed error count over time.

I'll look into it a bit more...