Fix pylint warnings

[MVrachev]

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Description of the changes being introduced by the pull request:

New pylint warnings appeared (for the first time here: https://github.com/theupdateframework/python-tuf/pull/1446/checks?check_run_id=3630842220) with code:
W0602: Using global for X but no assignment is done (global-variable-not-assigned)
where X is a global variable.
In the lines pointed by the warnings, "global" was used inside a
function scope in order to enable assignment of the global variable to
a new value in the function.
The reason for these warnings was that pylint noticed we are using
"global" for the variable X inside a function scope without actually
assigning it to a new value.
Overall that was true for the reported cases and I removed the use of
"global", but there were only two cases where pylint reported a
false-positive. Then we were using "global", but pylint didn't
understand there were assignments.
In those cases, I disabled the warnings.

Signed-off-by: Martin Vrachev mvrachev@vmware.com

Please verify and check that the pull request fulfills the following
requirements:

• The code follows the Code Style Guidelines
• Tests have been added for the bug fix or new feature
• Docs have been added for the bug fix or new feature

[coveralls]

Pull Request Test Coverage Report for Build 1246105286

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.162%

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Totals
Change from base Build 1245173711:	0.0%
Covered Lines:	3792
Relevant Lines:	3829

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💛 - Coveralls

[jku]

I looked at a few cases and pylint is correct: those globals are not needed.

global is only required if you want to assign to the global variable. mutating the value of that variable does not require global.

[jku]

https://www.programiz.com/python-programming/global-keyword

these third party documentation sites have really variable quality... The whole point of global is that assignment to global variables can only work with global, yet this is not mentioned at all.

I try to find references for this sort of things on python.org (the search engines really fail hard with python searches, always offering this sort of pages before python.org content)

[MVrachev]

I looked at a few cases and pylint is correct: those globals are not needed.

global is only required if you want to assign to the global variable. mutating the value of that variable does not require global.

Updated the pr and removed all but two occurrences of global which are false-positives.

these third party documentation sites have really variable quality... The whole point of global is that assignment to global variables can only work with global, yet this is not mentioned at all.

Yes, you are right. Removed the link from the commit message and pr description.

I try to find references for this sort of things on python.org (the search engines really fail hard with python searches, always offering this sort of pages before python.org content)

I can't find where on python org globals are mentioned and that's why I won't give a link.

[jku]

-55 lines, fixes CI

Nice