On Mon, Aug 9, 2021 at 1:42 PM wrote:

This is a proposal to change the behaviour of the startswith() and endswith() methods for str, bytes and bytearray objects, making them return the matched value instead of the True boolean.

Unfortunately this would break backward compatibility, since it's currently guaranteed that they return precisely True or False, and that can be used (eg) for indexing. To maintain that, you'd have to create new methods which return the matched value or None (and can then define startswith/endswith as the boolification of that). For instance: domain.findsuffix((".fr", ".com", ".org")) ChrisA

that can be used (eg) for indexing

Even without it being used in as complicated a way as that it's *still* not backward compatible because of the trivial case, as foo.endswith("") is True. On Sun, Aug 8, 2021 at 11:55 PM Chris Angelico wrote:

On Mon, Aug 9, 2021 at 1:42 PM wrote:

...

This is a proposal to change the behaviour of the startswith() and endswith() methods for str, bytes and bytearray objects, making them return the matched value instead of the True boolean.

Unfortunately this would break backward compatibility, since it's currently guaranteed that they return precisely True or False, and that can be used (eg) for indexing. To maintain that, you'd have to create new methods which return the matched value or None (and can then define startswith/endswith as the boolification of that). For instance:

domain.findsuffix((".fr", ".com", ".org"))

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On 2021-08-09 23:57:42, Chris Angelico wrote:

On Mon, Aug 9, 2021 at 10:32 PM Samuel Freilich wrote:

...

Even without it being used in as complicated a way as that it's still not backward compatible because of the trivial case, as foo.endswith("") is True.

I was talking specifically about the original, which can be depended upon to return True or False. Changing the return value would break anything that depends on that.

Not sure what you're referring to.

I think this is the problem:

...

...

...

"str".endswith("") is True True "" is True <stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="? False

Even if you use the return value as a bool, it will flip the result.

On Tue, Aug 10, 2021 at 12:03 AM Simão Afonso wrote:

On 2021-08-09 23:57:42, Chris Angelico wrote:

...

On Mon, Aug 9, 2021 at 10:32 PM Samuel Freilich wrote:

...

Even without it being used in as complicated a way as that it's still not backward compatible because of the trivial case, as foo.endswith("") is True.

I was talking specifically about the original, which can be depended upon to return True or False. Changing the return value would break anything that depends on that.

Not sure what you're referring to.

I think this is the problem:

...

...

...

...

"str".endswith("") is True True "" is True <stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="? False

Even if you use the return value as a bool, it will flip the result.

Yep, that's also a problem, but I don't understand why my comment about "can be used eg for indexing" was being quoted for context there. I was talking about how you could do something like this: protocol = ("ws:", "wss:")[url.startswith("https:")] If the return value changes, this breaks. ChrisA

09.08.21 17:05, fgallaire@gmail.com пише:

Two possibilities:

1) the perfectly backward compatible, retrun False 2) the more pythonic, return the empty value of the object (i.e. "" for str)

The problem is that for backward compatibility it should return True. And empty string's boolean value is false.

Excuse me, I wrote this answer from the web interface. Florent Le lun. 9 août 2021 à 16:16, Chris Angelico a écrit :

On Tue, Aug 10, 2021 at 12:08 AM wrote:

...

Two possibilities:

1) the perfectly backward compatible, retrun False 2) the more pythonic, return the empty value of the object (i.e. "" for str)

Please quote the person you're responding to, for context. Were you replying to Serhiy?

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