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Comment by hikarudo | Hacker News Reader

Sincere question: what's wrong with Python f-strings?

Three people in a row and not one of you guys checked out Swift strings before commenting, thus making exactly the mistake I complained about.

Look up Swift strings. Python has 4 types of string literals. Swift has 1. And they are BETTER and more powerful. Cleaner.

Swift has "normal strings", #"raw strings"#, and """ for multiline strings. For interpolation, it uses "The answer is \(1+2)", but in a raw string you need #"The answer is \#(1+2)"#.

So compared to Python, string interpolation is always "on" and doesn't need an f-prefix. Because it uses the string escaping syntax, it doesn't have to take over a regular character like {, which requires {{ escaping.

Is this supposed to be better than python? "Every string is an f-string, make sure you don't accidentally miss some interpolation." sounds like a step down, not like an improvement to me!

What do you mean by "miss some interpolation"?

There are two errors you could make in Python. Accidentally using {} in a normal string where you wanted interpolation, and accidentally using {} in an f-string where you wanted literal {}. I definitely do the former a lot.

The escape character is \. Same as in Python. But in Python you have to watch out for \ AND {. In Swift, only \.

And you can do this:

####"foo ###\(this is not interpolation) ####\(but this is) bar"####

In Pythons f-strings you can't ever write the literal `{foo}` in a string for documentation for example. It's a mess.

Close. But wrong.

Swift doesn't have raw strings and normal strings. Swift has ONE syntax:

{#n}"string {#n}\(interpolation)"{#*n}

Where n can be zero or more. So let's recap:

1. ONE rule for start/end/escape prefix: A number of # that has to match. 2. ONE rule for escape: \.

I do Python full time and I wouldn't consider switching to Swift, but the string situation is horrible compared to Swift.

Yes it does, because normal strings aren't just a special case of raw strings when the number of #s is 0. The presence of #s change the string syntax. Otherwise you could as well say Python has one syntax, with optional f and r prefixes.

No, you can't. Because r/f changes and/or adds escape sequences, AND you can't have double-raw strings for example. In Swift there's 0, 1, 2, 3, 4, etc number of #. It's not raw strings at all! There's no -1 number of #. So for example to do regexes in python you normally use r-strings, to avoid \ escaping in the regex. In Swift you could do the same the opposite way: not by removing \ escaping, but by changing it to \#. And if you want to regex match for \#, you can do ##. And if you want to match for \## you can use ###, etc.

There is always a clean escape where you can write the literal that you want to write. Unlike in Python where there is no escape (amusingly).

Ah, I see. That is better.

Yea, it's a super nice system. It's such a pity that most language designers don't look at other languages before implementing stuff.

I tried to warn the D guys not to make this exact mistake, but they didn't listen :/

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