Forbid a[len(a)-1]

[orsinium]

Rule request

Thesis

That's a common mistake of gophers. Golang has no negative index (yet?), but Python has.

Bad:

a[len(a) - 1]
a[len(a) + 1]  # IndexError

Good:

a[-1]
a[1]
a[len(a) // 2]

The floor division is ok. Plus len and minus len isn't

Reasoning

a[len(a)-1] is slow, a[len(a)+1] is IndexError.

[sobolevn]

Awesome!

[sobolevn]

@kxepal do you have any comments on this?

[ghost]

Can I take this?

[sobolevn]

Let's start with #861
Later you can take as many as you want 🙂

[lensvol]

Can I take this one?

[sobolevn]

Done! Thanks! 👍

[kxepal]

do you have any comments on this?

LGFM, except this case is quite rare one and mostly relates to migration from some Golang to Python. I can't find any similar issues in real Python code.

[sobolevn]

Hi @lensvol, how's it going? Do you need any help?

[lensvol]

Hi @sobolevn, everything is on track, got distracted by real-life issues sadly :/ Hope I will close it this week.