bpo-31504: Update stdtypes.rst

[kgashok]

Added behaviour of find when substring is "".

https://bugs.python.org/issue31504

[raulcd]

Hi @kgashok ,

Build is failing as this is not true:

Python 3.6.2 (default, Aug 23 2017, 13:37:24) 
[GCC 7.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 'abc'.find('')
0

[tiran]

Thanks for your contribution.

Your PR has multiple issues:

• Title of the ticket is not recognized by our bot. You need to add a colon after the bpo number: bpo-31504: Update stdtypes.rst
• Doc tests are failing. You added extra line.
• As @raulcd already pointed out, the patch is wrong.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I didn't expect the Spanish Inquisition!. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[merwok]

I think the text should explain why. As shows in the bpo-24243 ticket, people may be surprised by this behaviour if they don’t understand how it derives from Python’s notion of string slices. If you know that '' in 'abc' is true + the doc of str.find says it returns the highest index of the found substring, then this is not a surprise. I am not sure that mentioning len only here will help people make sense of it.

[merwok]

Notation note: let’s write code like len(s), not len(str).

[serhiy-storchaka]

Closed because tests failed, the added claim is not true, and the author is not active for a half of year.