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Comment by stavros | Hacker News Reader

Yeah, I generally like most of the stuff that goes into Python, but I have to admit I can't really see the usefulness in this (or, at least, enough usefulness to warrant making it standard).

One of the PEP's developers, Lysandros, presented this in our local meetup, so I am passingly familiar with it, but still, I might be missing something.

I guess the crux of it is that I don't understand why it's `t"some string"` instead of `Template("some string")`. What do we gain by the shorthand?

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> What do we gain by the shorthand?

Because it's new syntax, it allows for parsing the literal ahead of time and eagerly evaluating the substitutions. Code like

    bar = 42
    spam = t"foo {bar*bar} baz"

essentially gets translated into

    bar = 42
    spam = Template("foo ", Interpolation(bar*bar), " baz")

That is: subsequent changes to `bar` won't affect the result of evaluating the template, but that evaluation can still apply custom rules.

Ah OK, I see what you mean, so they're basically an f-string that hasn't been "baked in" yet, and you can still access all its parameters. That's pretty cool.

Yes, that's also a fine way to describe it IMO.

I guess this could be useful in SQL for escaping values, I saw a project on the comments here.

With templates:

  mysql.execute(t"DELETE FROM table WHERE id={id} AND param1={param1}")

Without templates:

  mysql.execute("DELETE FROM table WHERE id=%s AND param1=%s", [id, param1])

So one less argument to pass if we use templates.

But yeah it does seem a bit confusing, and maybe kinda not pythonic? Not sure.

SQL templating is one of the explicitly cited motivating use cases.

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