Fix performance in get_imports regexp

[AlekseyLobanov]

What does this PR do?

Just found that one of the Regular Expressions may be very slow (O(N^3)) on some special inputs.

Something like 'try:' + ' ' * 1500 may take a lot of time. I replaced it with the same logic but faster

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

@gante

[AlekseyLobanov]

It is not a typo but still a small change with existing tests

[Rocketknight1]

This looks good now! It should be simpler and more performant, and shouldn't change which strings it matches.

I have one more suggestion, though. This regex looks like it would fail in cases when the strings "try" and "except" occur internally in some lines. This is probably very rare, but maybe we should change the regex to \n\s*try and \n\s*except to be secure against that?

To be clear, this isn't a bug with your PR - it's an issue with the regex that already existed!

[AlekseyLobanov]

regex looks like it would fail in cases ...

Any regex should fail because even valid Python source is not defined by a regular language.
For example, code below also should be ignored, I believe.

"""
try:
    pass
except:
    pass
"""
# code in multi line string literal

Should I add it in another PR with more tests? This PR is more about performance improvements.

Maybe we can wait for @gante to reply, because he wrote this lines.

[Rocketknight1]

@AlekseyLobanov yes, good point - we can keep this PR simple. Want me to merge this one now, and if you think you can improve it further, you can open a new PR with added test(s)?

[AlekseyLobanov]

Want me to merge this one now, and if you think you can improve it further, you can open a new PR with added test(s)?

Can we just merge this for now? It will be great.

[gante]

Maybe we can wait for @gante to reply, because he wrote this lines.

Hehe not true (#23725 is the source of these lines), but the diff looks good to me :)

[Rocketknight1]

Yes, the diff looks good to me. Thanks for the PR!