On 5/7/19 8:39 PM, Steven D'Aprano wrote:
Disclaimer: this topic seems to have been split over at least two issues
on the bug tracker, a Python-Ideas thread from 2018, Discourse (I
think...) and who knows what else. I haven't read it all, so excuse me
if I'm raising something already discussed.
Yeah, it's all over the place. At this stage, I think discussing it here
is best.
On Mon, May 06, 2019 at 08:39:41PM -0400, Eric V. Smith wrote:
After that lightning talk, Larry and I talked about it some more, and
for a number of reasons decided that it would make more sense if the
syntax used an = sign. So we came up with f"{foo=}", which would also
produce "foo='Hello'".
The reasons for the change are:
- Having '=' in the expression is a better mnemonic than !d.
- By not using a conversion starting with !, we can compose = with the
existing ! conversions, !r, !s, and the rarely used !a.
- We can let the user have a little more control of the resulting string.
You're going to hate me for bike-shedding, but I really don't like using
= as a defacto unary postfix operator. To me, spam= is always going to
look like it was meant to be spam==<something> and the second half got
accidentally deleted.
I don't have a better suggestion, sorry.
I think = makes a great mnemonic for what's happening. I realize it
looks a little funny at first, but just wait until you start confusing
it with := (hah!). Everyone else I've discussed it with likes =.
In an earlier draft, back when this was spelled !d, you specifically
talked about whitespace. Does this still apply?
Yes, it does.
spam = 42
f'{spam=}' # returns 'spam=42'
f'{spam =}' # returns 'spam =42'
f'{spam = }' # returns 'spam = 42' I guess?
All correct.
f'{spam+1=}' # returns 'spam+1=41' I guess?
I'm not proposing to redefine addition by one, so this is actually
'spam+1=43' :)
Eric
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