On Wed, Oct 3, 2018 at 3:28 AM Eric V. Smith <e...@trueblade.com> wrote:
>
> Here’s the idea: for f-strings, we add a !d conversion operator, which
> is superficially similar to !s, !r, and !a. The meaning of !d is:
> produce the text of the expression (not its value!), followed by an
> equal sign, followed by the repr of the value of the expression. So:
> [...]
> The mnemonic is !d for “debugging”. I’d wanted to use !=, because
> there’s an equal sign involved in the result, but = is the one character
> that can’t be used after ! (it’s “not equal” in expressions, and
> f-strings look specifically for that case). I also mentioned !!, but I
> think I prefer !d as being less confusing.
>
> This would be used in debugging print statements, that currently end up
> looking like:
>
> print(f'value={value!r}')
>
> and would now be:
>
> print(f'{value!d}')
>
> There have been discussions about ways to specify str() vs. repr(),
> using characters other than '=', adding spaces, etc. But they all end up
> over-complicating what should be a simple tool, not a Swiss Army knife.
>
> Thoughts?
>
> Eric
I think the feature is useful to avoid re-typing the expressions.
But still, the syntax is a bit obscure, and the feature
is very limited (can't construct anything but "x=x").
That makes me personally less enthusiastic about using it instead
of the common: f" x = {x}". (yes I use spaces around = most of
the time and probably only spaces for table-like output)
Did you think about more general syntax for repetitions?
If there would be a way to repeat entries, one could do similar output
without much extra typing.
E.g. an asterisk for "same expression" ?
price = 10
s = f"{price} {*}" # 10 10
And then using say {expr !} would print _only_ the expression string.
So with e.g. some variable:
variable = 13.18654937
f"{variable !} = {*:.4f} {*:.2f} {*:.0f}"
prints:
variable = 13.1865 13.19 13
Something like that. It is more complex implementation, etc,
but has better, verbose appearance Imo and not so limited.
And custom formatting is important to achieve a readable output.
Mikhail
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