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As now f-strings can contain any valid Python expression inside expression components, it is now possible to nest f-strings arbitrarily: >>> f"{f"{f"{f"{f"{f"{

As now f-strings can contain any valid Python expression inside expression components, it is now possible to nest f-strings arbitrarily: >>> f"{f"{f"{f"{f"{f"{1+1}"}"}"}"}"}" '2' Is anyone aware of the change to the interpreter that allows for this?

striking 3y ago
At https://peps.python.org/pep-0701/#motivation https://peps.python.org/pep-0701/#motivation > When f-strings were originally introduced in PEP 498, the specification was provided without providing a formal grammar for f-strings. Additionally, the specification contains several restrictions that are imposed so the parsing of f-strings could be implemented into CPython without modifying the existing lexer. [...] > The other issue that f-strings have is that the current implementation in CPython relies on tokenising f-strings as STRING tokens and a post processing of these tokens. This has the following problems: [...] At https://peps.python.org/pep-0701/#rationale https://peps.python.org/pep-0701/#rationale > By building on top of the new Python PEG Parser (PEP 617), this PEP proposes to redefine “f-strings”, especially emphasizing the clear separation of the string component and the expression (or replacement, {...}) component.
DecoPerson 3y ago
JavaScript has this with template strings. I use it often: s = `something ${cond ? `(${v})` : ''} something`
mirekrusin 3y ago
js can do it $ node > `${`${`${1+1}`}`}` '2'
jhvkjhk 3y ago
Parse it recursively.
- mathisfun123 3y ago
  yup
vscode-plz-stop 3y ago
This has always worked in a Javascript. > `${`${`${`${`${1 + 1}`}`}`}`}` '2' It was simply a limitation with the Python parser. Heck, it even works in Vimscript :echo $'{$'{$'{1 + 1}'}'}' 2
JohnBooty 3y ago
Is it uncommon? Ruby does it in a fairly syntactically similar way: "Hello, it's #{"#{Time.now}"}" => "Hello, it's 2023-10-02 09:41:40 -0400"
mathisfun123 3y ago
just replace `f"{` -> `(` and `}"` -> `)` and it's conventional expression eval.
NegativeLatency 3y ago
Ruby can do this: > puts “h#{”#{i}”}” You “just” have to make your parser understand how to have all expressions or whatever inside braces. No idea how the python parser works but think about how you can nest json arbitrarily.
ShamelessC 3y ago
> Is anyone aware of the change to the interpreter that allows for this? Why answer your question when I could just brag about how my personal favorite language has supported this for awhile? /s
- seanw444 3y ago
  But did you know Javascript, Ruby, and Vimscript can already do it?
  - deleted 3y ago
    [deleted]

striking 3y ago

At https://peps.python.org/pep-0701/#motivation https://peps.python.org/pep-0701/#motivation > When f-strings were originally introduced in PEP 498, the specification was provided without providing a formal grammar for f-strings. Additionally, the specification contains several restrictions that are imposed so the parsing of f-strings could be implemented into CPython without modifying the existing lexer. [...] > The other issue that f-strings have is that the current implementation in CPython relies on tokenising f-strings as STRING tokens and a post processing of these tokens. This has the following problems: [...] At https://peps.python.org/pep-0701/#rationale https://peps.python.org/pep-0701/#rationale > By building on top of the new Python PEG Parser (PEP 617), this PEP proposes to redefine “f-strings”, especially emphasizing the clear separation of the string component and the expression (or replacement, {...}) component.

DecoPerson 3y ago

JavaScript has this with template strings. I use it often: s = `something ${cond ? `(${v})` : ''} something`

mirekrusin 3y ago

js can do it $ node > `${`${`${1+1}`}`}` '2'

jhvkjhk 3y ago

Parse it recursively.

mathisfun123 3y ago
yup

vscode-plz-stop 3y ago

This has always worked in a Javascript. > `${`${`${`${`${1 + 1}`}`}`}`}` '2' It was simply a limitation with the Python parser. Heck, it even works in Vimscript :echo $'{$'{$'{1 + 1}'}'}' 2

JohnBooty 3y ago

Is it uncommon? Ruby does it in a fairly syntactically similar way: "Hello, it's #{"#{Time.now}"}" => "Hello, it's 2023-10-02 09:41:40 -0400"

mathisfun123 3y ago

just replace `f"{` -> `(` and `}"` -> `)` and it's conventional expression eval.

NegativeLatency 3y ago

Ruby can do this: > puts “h#{”#{i}”}” You “just” have to make your parser understand how to have all expressions or whatever inside braces. No idea how the python parser works but think about how you can nest json arbitrarily.

ShamelessC 3y ago

> Is anyone aware of the change to the interpreter that allows for this? Why answer your question when I could just brag about how my personal favorite language has supported this for awhile? /s

seanw444 3y ago
But did you know Javascript, Ruby, and Vimscript can already do it?
- deleted 3y ago
  [deleted]