[Python-Dev] PEP-498: Literal String Formatting

[David Mertz]

Y'know, I just read a few more posts over on python-ideas that I had missed
somehow.  I saw Guido's point about `**locals()` being too specialized and
magical for beginners, which I agree with.  And it's the other aspect of
"magic" that makes me not like f-strings.  The idea of *implicitly* getting
values from the local scope (or really, the global_local_builtin scope)
makes me worry about readers of code very easily missing what's really
going on within an f-string.

I don't actually care about the code injection issues and that sort of
thing.  I mean, OK I care a little bit, but my actual concern is purely
explicitness and readability.

Which brought to mind a certain thought.  While I don't like:

    f'My name is {name}, my age next year is {age+1}'

I wouldn't have any similar objection to:

   'My name is {name}, my age next year is {age+1}'.scope_format()

Or

  scope_format('My name is {name}, my age next year is {age+1}')

I realize that these could be completely semantically equivalent... but the
function or method call LOOKS LIKE a runtime operation, while a one letter
prefix just doesn't look like that (especially to beginners whom I might
teach).

The name 'scope_format' is ugly, and something shorter would be nicer, but
I think this conveys my idea.

Yours, David...

On Sun, Aug 9, 2015 at 6:14 PM, David Mertz <mertz at gnosis.cx> wrote:

> On Sun, Aug 9, 2015 at 11:22 AM, Eric V. Smith <eric at trueblade.com> wrote:
>>
>> I think it has to do with the nature of the programs that people write.
>> I write software for internal use in a large company. In the last 13
>> years there, I've written literally hundreds of individual programs,
>> large and small. I just checked: literally 100% of my calls to
>> %-formatting (older code) or str.format (in newer code) could be
>> replaced with f-strings. And I think every such use would be an
>> improvement.
>>
>
> I'm sure that pretty darn close to 100% of all the uses of %-formatting
> and str.format I've written in the last 13 years COULD be replaced by the
> proposed f-strings (I suppose about 16 years for me, actually).  But I
> think that every single such replacement would make the programs worse.
> I'm not sure if it helps to mention that I *did* actually "write the book"
> on _Text Processing in Python_ :-).
>
> The proposal just continues to seem far too magical to me.  In the
> training I now do for Continuum Analytics (I'm in charge of the training
> program with one other person), I specifically have a (very) little bit of
> the lessons where I mention something like:
>
>   print("{foo} is {bar}".format(**locals()))
>
> But I give that entirely as a negative example of abusing code and
> introducing fragility.  f-strings are really the same thing, only even more
> error-prone and easier to get wrong.  Relying on implicit context of the
> runtime state of variables that are merely in scope feels very break-y to
> me still.  If I had to teach f-strings in the future, I'd teach it as a
> Python wart.
>
> That said, there *is* one small corner where I believe f-strings add
> something helpful to the language.  There is no really concise way to spell:
>
>   collections.ChainMap(locals(), globals(), __builtins__.__dict__).
>
> If we could spell that as, say `lgb()`, that would let str.format() or
> %-formatting pick up the full "what's in scope".  To my mind, that's the
> only good thing about the f-string idea.
>
> Yours, David...
>
> --
> Keeping medicines from the bloodstreams of the sick; food
> from the bellies of the hungry; books from the hands of the
> uneducated; technology from the underdeveloped; and putting
> advocates of freedom in prisons.  Intellectual property is
> to the 21st century what the slave trade was to the 16th.
>



-- 
Keeping medicines from the bloodstreams of the sick; food
from the bellies of the hungry; books from the hands of the
uneducated; technology from the underdeveloped; and putting
advocates of freedom in prisons.  Intellectual property is
to the 21st century what the slave trade was to the 16th.
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