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Python f-string quiz (fstrings.wtf)
submitted 1 year ago by to c/python@programming.dev
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[–] 29 points 1 year ago (2 children)

To be fair this was quite wtf-free. Mostly just unimportant formatting subtleties and stuff you'd never write.

Python definitely has bigger WTFs, like bool being an int, implicit bool conversion, implicit iteration of strings, etc.

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    • [–] 12 points 1 year ago*

    Hmm: 17/26

    Failures were:

    • didn't know about the = option, but once I saw it once, I guessed right a few times
    • never used ^ in Python, and didn't make the connection to XOR (I figured I'd need the math library or something)
    • the r and a with =! (again, never used = option)
    • edge cases in walrus operator and other things unrelated to f-strings

    Most of those I missed (and many I got) I'd reject a PR over because it's not obvious enough what's going on. But I think given that, I did reasonably well.

    But I learned something. Thanks for the post!

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    [–] 8 points 1 year ago (1 child)

    Your final score: 9/26

    There were more nuances and surprised than anticipated. But it should be expected, because its on this website. :D But any language with duck typing and lot of magic and interpretation, and a long history of changes and additions, used in a huge variety of environments, is bound to be surprising. I am not surprised that JavaScript and Python are surprising.

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  • [–] 2 points 1 year ago

    What to know about f strings

    !r is a thing

    !s is a thing

    There is some syntax for formatting a float which will completely be forgotten that'll have to be looked up.

    There is nothing else worth knowing.

    Now lets moan and complain about something actually important. Like repos with languishing PRs, like SQLModel.

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    • [–] 8 points 1 year ago

    This is fun, as was the JS date one. I hope people do more.

    Still though, I don't think doing well or not on these necessarily mean you're good or bad with the language.

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    [–] 4 points 1 year ago

    Tap for spoilersI was sure something was wrong with the first question, probably because of the linter in my editor.

    TIL about the feature in #4, it'll be handy in my day-to-day businesses.

    I forgot about the escaping in #7.

    #19: what?

    From then on, it was all [uneducated] guesses.

    12/26, need more practice.

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    [–] 7 points 1 year ago (6 children)

    Walrus operator. What did I just read?

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  • [–] 13 points 1 year ago (4 children)

    I love the walrus operator:

    if (x := some_function()):
    do_something(x)
else:
    # x is None or False or something, consider it invalid

    The only thing I wish was different is adding a scope, which would make x invalid outside the block. But Python's scoping rules are too dumb to handle this case.

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  • [–] 2 points 1 year ago (1 child)

    In lots of functional languages, you'd have some_function() return an Option type and then you'd use .map() or similar on it to only do something when the value is defined. I think, that can be done in Python's syntax, but you need a library for the Option type...

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  • [–] 3 points 1 year ago

    Python has an "Optional" type, but it's merely an alias for T | None. I wish Python had better support for FP, but each time it gets close, it doesn't quite go far enough.

    For example, it now has match blocks, but there's no error if the match is exhaustive, which hurts formal proofs of correctness. Likewise, tons of other features fall a bit short, but in general it's workable with some discipline.

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  • [–] 2 points 1 year ago

    I think my most common use case is with dictionary lookups.

    if (val := dct.get(key)) is not None:
    # do something with val

    I've also found some cases where the walrus is useful in something like a list comprehension. I suppose expanding on the above example, you you make one that looks up several keys in a dict and gives you their corresponding values where available.

    vals =  [val for key in (key1, key2, key3) if (val := dct.get(key)) is not None]
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  • [–] 2 points 1 year ago* (last edited 1 year ago)

    Walrus operator does an inline assignment to a variable and resolves to the value assigned. If it is in a condition statement, like "if x := y:", it assigns the value of y to x then interprets the expression of the condition as of it just said "if x:". Functionally, that means the assignment happens regardless of the value of y, but the condition only passes if the value of y is "truthy", i.e. if it's not None, an empty collection, numerically equal to zero, or just False.

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