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0 pointsGeorgeTirebiter4y ago0 comments

Indeed, if "{value} is bad" can be automatically f-stringed by an external program automatically --- then why can't Python do this automatically -- so we can get rid of the f-string type as a required explicit declaration? After all, we don't specifically add a type to a number like 42 or 3.14159 --- those are implicitly 'int' and 'float' types.

I would use such a feature, as I always use f-strings when formatting.

0 comments

masklinn4y ago

> Indeed, if "{value} is bad" can be automatically f-stringed by an external program automatically --- then why can't Python do this automatically -- so we can get rid of the f-string type as a required explicit declaration?

Because it would break existing strings containing braces, such as those used with `str.format`, or string.Template, or literal Jinja templates, ...

GeorgeTirebiterOP4y ago

Yes, my use case was "I always use F-strings" so these other breakages could not occur, by definition.

I suppose it's not that much of a problem to run a program to preprocess source and add in the F

But.. Python has a history of introducing new features that break old ones. That seems to me a balance between backward compatibility and future goodness.

the "from future import auto-fstring" construct could do it...

And, as for having to run the f-string parser: yes, but only once on static strings, which are most of them.

2 more replies

dragonwriter4y ago

If all strings with what looks like format specs are implicitly f-strings, how do you use reusable template strings, which use the same basic internal syntax, for formatting?

f-strings, like r-strings, have uses, but, like r-strings, I wouldn't want to replace plain strings with them.

ArchOversight4y ago

Because in some cases it is not desired, if for example the string is used in something that expands it further down the line (think SQL injection potential).

bagels4y ago

Backwards compatibility for one. Code existed before fstrings that may use curly braces, and you can currently use curly braces in non fstrings without escaping them.

Might also be a performance penalty for always having to run the fstring parser.

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