gh-65697: Prevent configparser from writing keys it cannot properly read

[lincolnj1]

Prevents configparser from writing keys containing delimiters and keys beginning with the section header pattern to a file.

Both of those scenarios create .ini files the parser cannot accurately read back. Keys beginning with the section header pattern parse back as new sections. Keys containing delimiters parse back only the first portion as a key and the remainder as a value (i.e. key: 'one=two', value:'three' writes as 'one=two=three' and parses back as key: 'one', value: 'two=three').

Unsure on whether to handle newlines in key/section/values by rejecting them when writing, rejecting them when set, or escaping them when writing.

• Issue: configparser accepts invalid keys and sections when writing #65697

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[jaraco]

The implementation looks sound and the tests seem to capture the essence of the change. I like it.

The only thing I'd like to see before accepting this - is there any lingering controversy? Who might oppose this change and can we get their consent?

If we can get consent from one or two of the most vocal detractors in the linked issues, then I'd say we could proceed. Otherwise, I'd like to hear their argument for what they recommend instead. Can you help gather that consensus?

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