feat(mypy): complete mypy support for the entire codebase

[mploski]

Issue #, if available:
aws-powertools/powertools-lambda#3

Description of changes:

• Fix all typing errors discovered by mypy
• Enable mypy in CI

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[mploski]

@heitorlessa github ci failing on the last error: https://github.com/mploski/aws-lambda-powertools-python/runs/4759867427?check_suite_focus=true.

I’d like to discuss a potential solution to this. In general mypy complains on subclass overwriting superclass get method with different signatures, which I believe breaks Liskov Substitution Principle. Other errors were solved already.

[mploski]

@heitorlessa github ci failing on the last error: https://github.com/mploski/aws-lambda-powertools-python/runs/4759867427?check_suite_focus=true.

I’d like to discuss a potential solution to this. In general mypy complains on subclass overwriting superclass get method with different signatures, which I believe breaks Liskov Substitution Principle. Other errors were solved already.

Since any change to this method's spec may be breaking to users and we cannot also move get method declaration in Base class to subclass for the same reason decided to silent it and accept potential risk

[codecov-commenter]

Codecov Report

Merging #943 (82d93fc) into develop (c43a5e8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #943   +/-   ##
========================================
  Coverage    99.96%   99.96%           
========================================
  Files          119      119           
  Lines         5320     5337   +17     
  Branches       613      608    -5     
========================================
+ Hits          5318     5335   +17     
  Partials         2        2           

Impacted Files	Coverage Δ
aws_lambda_powertools/event_handler/api_gateway.py	100.00% <100.00%> (ø)
aws_lambda_powertools/metrics/metrics.py	100.00% <100.00%> (ø)
aws_lambda_powertools/shared/functions.py	100.00% <100.00%> (ø)
...ws_lambda_powertools/utilities/batch/exceptions.py	100.00% <100.00%> (ø)
aws_lambda_powertools/utilities/batch/sqs.py	100.00% <100.00%> (ø)
...da_powertools/utilities/idempotency/idempotency.py	100.00% <100.00%> (ø)
...wertools/utilities/idempotency/persistence/base.py	99.36% <100.00%> (-0.01%)	⬇️
aws_lambda_powertools/utilities/parameters/base.py	100.00% <100.00%> (ø)
aws_lambda_powertools/utilities/parameters/ssm.py	100.00% <100.00%> (ø)
...bda_powertools/utilities/parser/envelopes/apigw.py	100.00% <100.00%> (ø)
... and 15 more

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[heitorlessa]

Thanks a lot @mploski - it covers a lot of ground and tech debt.

I'd like to ask you to consider two key aspects:

• Consider cast your last resource. cast is gonna increase the execution time for end-customers, and it slowly litters the code (similar to type coercion in other languages). Sometimes propagating the type, a generic, or creating another variable and an explicit type is a solution.
• Consider documenting beyond typing changes. I've noticed that we seem to be introducing a new bug in Idempotency by fixing a type, as we're changing a branching logic too. There are major block changes in Parameters too. For quick notes, use the PR description, and for larger ones like parameters comment on why this is necessary. Mypy can't see beyond the types, and while we have multiple checks in place we might slip a regression here. By changing that code, it'd be great to check whether additional tests are necessary too as we might have not covered that.

[mploski]

@heitorlessa Added few tests to fix tests coverage

[heitorlessa]

Added the last bits - thank you so so much again @mploski ;) A new era for Powertools. We must also keep a close eye after the release to see if this accidentally introduced any new bug that our checks + peer review wasn't able to detect.