On 5/9/18 9:28 AM, Chris Angelico wrote:
On Wed, May 9, 2018 at 11:06 PM, Steven D'Aprano <st...@pearwood.info> wrote:
On Wed, May 09, 2018 at 09:39:08AM -0300, Facundo Batista wrote:
This way, I could do:
authors = ["John", "Mary", "Estela"]
"Authors: {:, j}".format(authors)
'Authors: John, Mary, Estela'
Looks interesting, but I think we need to know the semantics in more
detail. For example:
- if the items of the list aren't already strings, how are they
converted?
I'd expect that they'd be converted using format(), which by default
would just call str(). How you'd go about specifying a format string,
though, I'm not sure.
- do you truly mean lists *only*, or is any iterable acceptible?
With the letter being "j" and the semantics being lifted from
str.join(), I would guess the latter.
Since '{:spec}'.format(obj) basically becomes obj.__format__('spec'),
this would have to be implemented on a concrete type (in the above
example, list).
From the sound of it, this would be a change made to format(), or
rather the underlying C level function, PyObject_Format(). If done
there, it would also automatically apply to f-strings and anything
else that calls format(). Perhaps the right way is not a colon marker,
but an enhancement to the ! notation? We currently have !s and !r to
do str() and repr(), and this could be !j followed by a join string.
Combining this with a colon would allow the individual elements to be
formatted with the given string, and then joined. For instance:
I would object to changing the format machinery. Any format spec should
be interpreted by some object's __format__ method.
Eric
x = [1,2,3]
msg = '#{x:3d!j, }#'.format(x=x)
# or equivalently
msg = f'#{x:3d!j, }#'
assert msg == '# 1, 2, 3#'
+0.5 on this. I don't currently yearn for it, but I'd probably use it
if it were available.
ChrisA
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