[Python-3000] String formating operations in python 3k

[Ian Bicking]

Barry Warsaw wrote:
> On Mon, 2006-04-03 at 23:43 +1000, Nick Coghlan wrote:
> 
> 
>>What do you think of a "format" builtin function that accepts the format as 
>>the first argument (similar to printf).
>>
>>The version on my harddrive permits positional arguments via $1, $2, etc, as 
>>well as string formatting (by sticking the format code in square brackets 
>>between the $ and the identifier). Keyword arguments still work, naturally.
>>
>>And if you don't want formatting, you just leave out the square brackets.
> 
> 
> I'm not totally sure I would need a builtin.  If I look at the two
> sources of $-strings in an app like Mailman, I'll see 1) literal human
> readable/translatable strings in the source code, 2) human entered
> strings that come from a web form.
> 
> In the first case, all string formatting will funnel through one
> bottleneck function, which will do the catalog lookup, frame variable
> discovery, and substitution all in one fell swoop.  So there, the
> builtin doesn't buy you much convenience.

Well, error messages are a common place I use %.  So:

assert path.startswith(prefix), (
     "%r should start with %r" % (path, prefix))
assert path.startswith(prefix), (
     $"${repr(path)} should start with ${repr(prefix)}")
assert path.startswith(prefix), (
     "$path should start with $prefix".substitute(
     path=repr(path), prefix=repr(prefix))


The second example assumes that you can include full expressions, 
otherwise that example would start looking really unpleasant.  As it is, 
the first example still looks more-or-less the best, and it's too bad 
$-based substitution doesn't include it.  I'm not sure how it would 
include it, unless there was something like $=path, or $<path>, or 
$`path` or something.  I dunno, none of those are very appealing.

str.substitute isn't too bad, except that "substitute" feels a little 
long-winded (compared to, say, str.format).  If "$path".format() worked, 
that'd be nice, but even though it's not that hard to implement, it 
breaks a lot of expectations.

Anyway, that's one example.  Any non-i18n'd code will likely have a fair 
amount of string substitution which isn't otherwise wrapped in any routines.

-- 
Ian Bicking  /  ianb at colorstudy.com  /  http://blog.ianbicking.org