Understanding Python through its builtins

Post by Xavdidtheshadow » Sun, Oct 10, 2021, 8:35 PM UTC

canjobear wrote: post #35

Alex3917 wrote: post #31

Earlier quoted context omitted.

> things like `.append` changing the object, returning `None` instead of creating a copy and returning that The obvious question is why it can't return a reference to the list instead of returning None. I feel like if I've been using the language on an almost daily basis for ten years now and I still get burned by that all the time, then it's just a poorly designed feature.

The advantage of mutating operations always returning None is that you can easily tell whether a mutation is happening by looking at the code. If you see y = f(x) that means x is unchanged, whereas if you see just f(x) on a line that means something stateful is happening.

Post by weatherlight » Sun, Oct 10, 2021, 8:50 PM UTC

matsemann wrote: post #62

> List comprehensions are basically a more Pythonic, more readable way to write these exact same things More pythonic maybe, but you can't have more than a single expression in a list comprehension without it becoming completely unintelligible. I also often miss other standard list features. Reduce, flatmap, indexed versions, utils like first of predicate, split, filternonnull etc

Post by weatherlight » Sun, Oct 10, 2021, 8:55 PM UTC

matsemann wrote: post #64

weatherlight wrote: post #63

Earlier quoted context omitted.

Anything remotely interesting like that is dumped in itertools. Python's creator, Guido van Rossum, doesn't like functional/functional-ish programming a lot. That's well-known. Guido: "I value readability and usefulness for real code. There are some places where map() and filter() make sense, and for other places Python has list comprehensions. I ended up hating reduce() because it was almost exclusively used (a) to…

Yes, lots of them are available. But I also would like to be able to call .sum() on my iterable at the end of a chain, instead of having to mentally unwrap sum(map(filter(filter(map(...))))

Post by escanor » Sun, Oct 10, 2021, 8:57 PM UTC

Post by dmurray » Sun, Oct 10, 2021, 8:59 PM UTC

Xavdidtheshadow wrote: post #61

canjobear wrote: post #35

Earlier quoted context omitted.

The advantage of mutating operations always returning None is that you can easily tell whether a mutation is happening by looking at the code. If you see y = f(x) that means x is unchanged, whereas if you see just f(x) on a line that means something stateful is happening.

I really like ruby's method naming convention for this: * `sort(arr)` returns a sorted copy of the input * `sort!(arr)` returns the sorted original methods that return booleans end in `?`, like `arr.sorted?` It's just a convention, but it's a nice way to let the writer know what will happen.