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I'm not sure if t-strings help here? unless I misread the PEP, it seems like they still eagerly evaluate the interpolations.

There is an observation that you can use `lambda` inside to delay evaluation of an interpolation, but I think this lambda captures any variables it uses from the context.

▲ actinium226 9 days ago | parent | next [-]

> There is an observation that you can use `lambda` inside to delay evaluation of an interpolation, but I think this lambda captures any variables it uses from the context.

Actually lambda works fine here

    >>> name = 'Sue'
    >>> template = lambda name: f'Hello {name}'
    >>> template('Bob')
    'Hello Bob'

▲ davepeck 9 days ago | parent | prev | next [-]

> I'm not sure if t-strings help here?

That's correct, they don't. Evaluation of t-string expressions is immediate, just like with f-strings.

Since we have the full generality of Python at our disposal, a typical solution is to simply wrap your t-string in a function or a lambda.

(An early version of the PEP had tools for deferred evaluation but these were dropped for being too complex, particularly for a first cut.)

▲

krick 9 days ago | parent [-]

And that actually makes "Template Strings" a misnomer in my mind. I mean, deferred (and repeated) evaluation of a template is the thing that makes template a template.

Kinda messy PEP, IMO, I'm less excited by it than I'd like to be. The goal is clear, but the whole design feels backwards.

	▲	davepeck 9 days ago \| parent [-]
		Naming is hard; for instance, JavaScript also has its own template strings, which are also eagerly evaluated.

▲ notpushkin 9 days ago | parent | prev | next [-]

> An early version of this PEP proposed that interpolations should be lazily evaluated. [...] This was rejected for several reasons [...]

Bummer. This could have been so useful:

    statement_endpoint: Final = "/api/v2/accounts/{iban}/statement"

(Though str.format isn’t really that bad here either.)

▲ nhumrich 9 days ago | parent | next [-]

There was a very very long discussion on this point alone, and there are a lot of weird edge cases, and led to weird syntax things. The high level idea was to defer lazy eval to a later PEP if its still needed enough.

There are a lot of existing workarounds in the discussions if you are interested enough in using it, such as using lambdas and t-strings together.

▲ LordShredda 9 days ago | parent | prev | next [-]

Would be useful in that exact case, but would be an absolute nightmare to debug, on par with using global variables as function inputs

	▲	notpushkin 9 days ago \| parent [-]
		Yeah, to be honest, every time this comes to mind I think “wow, this would be really neat!”, then realize just using .format() explicitly is way easier to read.

▲ o11c 9 days ago | parent | prev [-]

I do think that people are far too hesitant to bind member functions sometimes:

  statement_endpoint: Final = "/api/v2/accounts/{iban}/statement".format

(it's likely that typecheckers suck at this like they suck at everything else though)

▲ tylerhou 9 days ago | parent | prev | next [-]

You could do something like t”Hello, {“name”}” (or wrap “name” in a class to make it slightly less hacky).

▲ skeledrew 9 days ago | parent | prev [-]

Lambda only captures variables which haven't been passed in as argument.