Solution: add another CI environment: CircleCI

- Refactor complex statement to use if expression.
- Fix dangerous default argument.
- Remove unused imports and reimported modules.
- Refactor unnecessary use of list comprehension.
- Add .deepsource.toml file for continuous analysis on bug risks/performance/code-quality issues on new changes.

Solution: avoid using encrypted variables when on PR

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Solution: make them more explicit

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Solution: document it.

Solution: expand it to sthing more detailed

Solution: create missing dir before `os.rename`

Solution: login to docker hub

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Solution: use new advised URLs

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and wheels in developement

Solution: show used versions

Solution: use packaging APIs

Solution: add it

Solution: test when configs that are extended increment a key
with no original value

Solution: install glibc-langpack

Solution: rename variable for better readability

remove useless deepcopys since _update does it properly now

Solution: return new dict to avoid subtle bugs

Solution: merge default_cfg in the first config without extends

because it is the cause for subtle bugs

Solution: return copies of object rather than mutating

Solution: move to directory
starts to chop into pieces

Solution: add tests that shows there are no issues

Solution: remove them

Solution: enables more than one digit

Solution: use environment variable instead

- fix bootstrapping for Python 2.7

The bootstrap process uses `get-pip.py`, which in its latest version,
tries to bootstrap a Python 3 only version of pip.

We need to pass in a separate URL for a Python 2.7 compatible version of
get-pip.py.

- Handle different pip messages

e.g. on pip 20.3.4 the message for no updates is
"Requirement already up-to-date"

e.g. on pip 21.0.1 the message for no updates is
"Requirement already satisfied"

Co-authored-by: Michael Howitz <mh@gocept.com>

Solution: stop monitoring setuptools head with 2.7

Solution: update to latest

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