[Python-ideas] Dart like multi line strings identation
steve at pearwood.info
Sat Mar 31 20:43:30 EDT 2018
On Sat, Mar 31, 2018 at 04:50:03PM +0200, Marius Räsener wrote:
> What I have in mind is probably best described with an Example:
> I am a
> the closing quote defines the "margin indentation" - so in this example all
> lines would get reduces by their leading 4 spaces, resulting in a "clean"
> and unintended string.
Backwards compatibility rules this out. I have many strings that
intentionally include indents and you will annoy me no end if you
make those indents disappear :-)
But having said that, for every one of those, I have a lot more where
the indents are annoying. I either outdent the lines:
text = """some text
and a third one
or I use implicit string concatenation:
text = ("some text\n"
"and a third\n")
neither of which I'm really happy with.
The ideal solution would:
- require only a single pair of starting/ending string delimiters;
- allow string literals to be indented to the current block, for
the visual look and to make it more convenient with editors
which automatically indent;
- evaluate without the indents;
- with no runtime cost.
One solution is to add yet another string prefix, let's say d for
dedent, but as Terry and others point out, that leads to a combinational
explosion with f-strings and r-strings already existing.
Another possibility is to make dedent a string method:
text = """\
and a third
and avoid the import of textwrap. However, that also imposes a runtime
cost, which could be expensive if you are careless:
for x in seq:
for y in another_seq:
some large indented string
(Note: the same applies to using textwrap.dedent.)
But we could avoid that runtime cost if the keyhole optimizer performed
the dedent at compile time:
triple-quoted string literal
could be optimized at compile-time, like other constant-folding.
Out of all the options, including the status quo, the one I dislike the
least is the last one:
- make dedent a string method;
- recommend (but don't require) that implementations perform the
dedent of string literals at compile time;
(failure to do so is a quality of implementation issue, not a bug)
- textwrap.dedent then becomes a thin wrapper around the string method.
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