On Another Subject, we could also have a language change staying that those
two lines are equivalent :
something"hello"
something("hello")
So that, any callable in the context can be used as a prefix ?
On Tue, Aug 27, 2019, 01:11 <stpa...@gmail.com> wrote:
> In Python strings are allowed to have a number of special prefixes:
>
> b'', r'', u'', f''
> + their combinations.
>
> The proposal is to allow arbitrary (or letter-only) user-defined prefixes
> as well.
> Essentially, a string prefix would serve as a decorator for a string,
> allowing the
> user to impose a special semantics of their choosing.
>
> There are quite a few situations where this can be used:
> - Fraction literals: `frac'123/4567'`
> - Decimals: `dec'5.34'`
> - Date/time constants: `t'2019-08-26'`
> - SQL expressions: `sql'SELECT * FROM tbl WHERE a=?'.bind(a=...)`
> - Regular expressions: `rx'[a-zA-Z]+'`
> - Version strings: `v'1.13.0a'`
> - etc.
>
> This proposal has been already discussed before, in 2013:
>
> https://mail.python.org/archives/list/python-ideas@python.org/thread/M3OLUURUGORLUEGOJHFWEAQQXDMDYXLA/
>
> The opinions were divided whether this is a useful addition. The opponents
> mainly argued that as this only "saves a couple of keystrokes", there is no
> need to overcomplicate the language. It seems to me that now, 6 years
> later,
> that argument can be dismissed by the fact that we had, in fact, added new
> prefix "f" to the language. Note how the "format strings" would fall
> squarely
> within this framework if they were not added by now.
>
> In addition, I believe that "saving a few keystroked" is a worthy goal if
> it adds
> considerable clarity to the expression. Readability counts. Compare:
>
> v"1.13.0a"
> v("1.13.0a")
>
> To me, the former expression is far easier to read. Parentheses,
> especially as
> they become deeply nested, are not easy on the eyes. But, even more
> importantly,
> the first expression much better conveys the *intent* of a version string.
> It has
> a feeling of an immutable object. In the second case the string is passed
> to the
> constructor, but the string has no meaning of its own. As such, the second
> expression feels artificial. Consider this: if the feature already
> existed, how *would*
> you prefer to write your code?
>
> The prefixes would also help when writing functions that accept different
> types
> of their argument. For example:
>
> collection.select("abc") # find items with name 'abc'
> collection.select(rx"[abc]+") # find items that match regular
> expression
>
> I'm not discussing possible implementation of this feature just yet, we
> can get to
> that point later when there is a general understanding that this is worth
> considering.
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