bpo-24612: Improve syntax error for 'not' after an operator

[pablogsal]

https://bugs.python.org/issue24612

[serhiy-storchaka]

It introduces misleading errors:

>>> not 1 */ 2
  File "<stdin>", line 1
    not 1 */ 2
    ^^^^^
SyntaxError: 'not' after an operator must be parenthesized

[serhiy-storchaka]

>>> not 1 +
  File "<stdin>", line 1
    not 1 +
    ^^^^^
SyntaxError: 'not' after an operator must be parenthesized

[pablogsal]

@serhiy-storchaka I have adapted the rule and added some extra tests, although I am a bit suspicious that this will be a bit tricky to get fully right.

[github-actions[bot]]

This PR is stale because it has been open for 30 days with no activity.

[bedevere-bot]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[encukou]

Would it make sense to additionally add a rule that will catch this for unary ops?

Yes. Do you want to add that to this PR?

[lysnikolaou]

Do you want to add that to this PR?

Done.

[encukou]

Thank you!