On 4/1/2018 8:55 AM, Chris Angelico wrote:
On Sun, Apr 1, 2018 at 10:36 PM, Steven D'Aprano <steve@pearwood.info> wrote:
And that *mental complexity* is (in my opinion) the biggest issue with adding a new d-prefix, and why I would rather make it a method.
Another big advantage of a method is that we can apply it to non-literals too.
I'd like to expand on this a bit more.
Current string prefix letters are:
* u/b: completely change the object you're creating * f: change it from a literal to a kind of expression * r: change the interpretation of backslashes * triple quotes: change the interpretation of newlines
All of these are significant *to the parser*. You absolutely cannot do any of these with methods (well, maybe you could have u/b done by having a literal for one of them, and the other is an encode or decode operation, but that's a pretty poor hack).
The one place where a dedented string would come in handy, and where it would need to be recognized by the parser (and could not be the result of a function or method) is a docstring. Well, I guess you could have the parser "know" about certain string methods, but that seems horrible. Eric
But dedenting a string doesn't change the way the source code is interpreted. So it's free to be a method - which is far easier to add to the language. All you need is ".dedent()" to be syntactically parsed as a method call (which it already is), and every tool that processes Python code will correctly interpret this.
So here's what, IMO, Marius can push for:
1) A method on Unicode strings which does the same as textwrap.dedent() 2) A peephole optimization wherein certain methods on literals get executed at compile time.
The latter optimization would also apply to cases such as " spam ".strip() - as long as all it does is return another constant value, it can be done at compile time. Semantically, though, the part that matters is simply the new method. (Sadly, this can't be applied to Decimal("1.234"), as that's not a method and could be shadowed/mocked.)
While I wouldn't use that method much myself, I think it's a Good Thing for features like that to be methods rather than functions stashed away in a module. (How do you know to look in "textwrap" for a line-by-line version of x.strip() ??) So I would be +1 on both the enhancements I mentioned above, and a solid -1 on this becoming a new form of literal.
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