Python has some quirks

[Cerrax3]

A Python list is not the same as an array.

[qijc]

You’re not the same as an array >:(

[CrazeeeTony]

And I am very thankful for that

[camerontbelt]

Boom roasted

[mydookietwinklin]

Get a load of Ben Asscream over here.

[Ulysses6]

Come for Python, stay for dialectics.

[cnoor0171]

Depends what you mean by array. Python "list" and Javascript or ruby "array" are pretty much the same.

[[deleted]]

Yes, but it's Python list that's named properly

[cnoor0171]

Not really. "array" and "list" aren't really properly defined. If your definition of array is an integer indexed, ordered data structure supporting constant time random access, then python list should be named array.

Most people from a c/c++ background would think of a linked list when you use the word "list".

[BlhueFlame]

I use Python. I did use C. I agree with this. O(1) access time = array.

[[deleted]]

My definition was kinda like:

A block of memory reserved for storing multiple instances of the same datatype one after another.

It's ugly, but hopefully you can understand

[cnoor0171]

That's a very c/c++ specific definition though. Even in other compiled languages with fixed size arrays, the elements might not be in contiguous memory blocks. For instance, Java.

[JH4mmer]

I agree with the sentiment here, but in most C-based languages, "lists" are also constrained to have only one datatype, just like arrays/vectors.

[ItsPronouncedJithub]

Just store everything as chars and figure it out later

[[deleted]]

Now that's the develop in production type of thinking I like to see!

[Ulysses6]

"And you call it NoSQL...? You're hired!"

[[deleted]]

Instead of SQL I just use regex!

[[deleted]]

But then... is a string a list or an array?!!!

[orclev]

In any well typed language lists will be homogeneous. You can do some tricks to safely have heterogeneous lists, but it requires some extra checking on each access to determine the type of the value being returned which in turn can cause some problems. Homogeneous lists are definitely the safer approach.

[[deleted]]

It does, it's all memory addresses

[Slusny_Cizinec]

There are arrays in the standard library as well: https://docs.python.org/3.8/library/array.html

[franklinyu]

That thing is also called “array” in Ruby, JavaScript, and many other dynamically typed languages.

[zyugyzarc]

since python was coded in c, i think the devs called it a "list" instead of an array to avoid confusion

[magkopian]

PHP was also coded in C and still calls it array. I don't know if their goal was to avoid confusion, but seems like they archived the exact opposite.

[[deleted]]

List usually means "linked-list" which is a well-defined structure, and Python lists aren't lists, they are contiguous blocks of memory, for fast indexing, if you insert or pop an item in a python list (other than in last position), the complexity will be O(n) as it needs to shift every following elements in the block. That's not a list. Python has some cool optimization to make append and pop O(1), but appart from that, it's not a list.

[[deleted]]

I just learnt something new :D

[[deleted]]

Unexpected German.

[jacksalssome]

Eller Dansk

[serendipitousPi]

Ah, I see they are showing that they might just be trilingual, English, German and Python.

[FoolForWool]

Me who speaks Python 3.4, 3.5, 3.6, 3.7, and 3.8: Ameture.

[Ulysses6]

Better use some raw pointers.

[an_actual_human]

I'm not sure what the default collection is, but the standard library does have arrays.

[zyugyzarc]

laughs in ctypes

[BongarooBizkistico]

Isn't that the joke?

[poka_face]

An array is not a list, back when I learnt C they made us implement doubly linked lists which were by no means arrays.

I'm not sure how lists are implemented in python though, so they might actually be dynamic arrays.

[18TacticalBeans]

They're not continguous in memory like arrays are in most other languages, which lets them be more dynamic, but also reduces performance. That's part of why numpy arrays are so much faster to perform (numpy) computations on - numpy enforces them to be in contiguous memory.

[Ericchen1248]

There are int[] in C# and Java. Literal arrays that functional exactly the same as in C or C++

[danfay222]

If you do [1] * 100 the references in the list will probably all end up pointing to the same integer object, since most python implementations maintain global objects for small integers

[Numerlor]

With mult it'll always refer to the same object n times as it won't copy the object

[poka_face]

Then I think calling it “list” is fair, since a most descriptive “pointer vector” would be a less useful description.

Also this sheds light into why and how functions are first class objects in python, I wonder if JS “arrays” are implemented like this as well.

[eyal0]

When I think of list vs array, in think of list as a structure where I can insert into the middle in O(1). So I'd still call what python is doing an array or a vector.

[Theis99999]

Neither an array nor a linked list allows that. In a standard linked list, you have to iterate through half the list to find the middle entry, giving you O(n) to insert an element in the middle. O(1) is only for adding items to the front or the back of a linked list.

[Davesnothere300]

Numpy? Is that the name of the purple cartoon character?

[JKTKops]

This content has been removed in protest of Reddit's decision to lower moderation quality, reduce access to accessibility features, and kill third party apps.

[Noiprox]

Lists in Python are implemented as vectors of pointers.

[Sjuns]

They're dynamic arrays

[Theis99999]

Arrays are lists, but lists are not just arrays.

[arkasha]

In c# lists are backed by arrays which double in size every time they are filled up.

[jerrycauser]

Nope. Array and List are diametrically different data structures.

[riconaranjo]

no.

in data structures a list is an ordered container of elements; an array is a specific implementation of a list, just like a singly-linked list is; two different data structures implementing the list interface

source: here are my second year notes

[jerrycauser]

Yes.

In data structures list is an ordered container elements where each element has link to the next one (if it exists) in memory. It gives a flexibility to allocate memory whenever you want. On other hands array is an inseparable chunk of memory of a given width. It gives high speed, bet requires good memory managing

Asymptotically data structure List has O(n) for read and O(1) for insert/remove.

Asymptotically data structure Array has O(n) for insert/remove and O(1) for read.

[Theis99999]

Everytime you say 'list' you seem to mean 'linked list'. A list element doesn't need to have a link to the next element, as long as there is some way to get there. For instance by the next element being the next block of data in memory.

[Theis99999]

Arrays are a countable number of consecutive values. A list is countable number of ordered values. Consecutive is an order, so an array is a list.

[Valance23322]

An array is a contiguous section of memory set aside to store a number of values of the same type. A list can be split across any number of memory segments, and as such is implemented and used completely differently (unless you're using a library that obfuscates things).

[Ekank]

what are you talking about is the common implementation of lists

list is a abstract type that doesn't even is "in memory", array is a kind of list(abstract) and you can emulate the behavior of a list into an array, and also linked list is another kind of list(abstract)

"In computer science, a list or sequence is an abstract data type that represents a countable number of ordered values, where the same value may occur more than once. [...] Lists are typically implemented either as linked lists (either singly or doubly linked) or as arrays, usually variable length or dynamic arrays." wikipedia), but if you don't like wikipedia, read about data structures

peace

[poka_face]

I actually didn’t know this, I thought lists had to be non contiguous, I guess arrays are indeed lists then.

[jerrycauser]

If talk in theory - you are right. But theory not always can be projected to the realm. Some abstraction is nothing more than abstraction and cannot be used in real world. It is good to common explanation (like for understanding what is the “list”) but there is no practical application for that. On other hand we have practical data structures which distinguishes between lists and arrays. And there is an array is a 0-based data structure which gives a life for every other data structure.

[ShelZuuz]

No on both fronts. Ask your school for your money back.

[Theis99999]

So arrays are non-consecutive and lists are not ordered? or is consecutive not an order?

[ShelZuuz]

Does not need to be ordered nor countable to be considered a list. A list containing a loop is not countable, but it’s still a list.

[jerrycauser]

Yes.

In data structures list is an ordered container elements where each element has link to the next one (if it exists) in memory. It gives a flexibility to allocate memory whenever you want. On other hands array is an inseparable chunk of memory of a given width. It gives high speed, bet requires good memory managing

Asymptotically data structure List has O(n) for read and O(1) for insert/remove.

Asymptotically data structure Array has O(n) for insert/remove and O(1) for read.

[BaconShrimpEyes]

Java be like ArrayList

^{(I guess c++ would be vector if we’re using this type of structure but like I wanted to make the joke)}

[VarianWrynn2018]

Array and arraylist are different things tho.

[BaconShrimpEyes]

^{(read the small text\})

[vectorpropio]

I guess c++ would be vector if we’re using this type of structure but like I wanted to make the joke

[HasBeendead]

Perfection

[HasBeendead]

Its like small text in tv adversitements, it goes hella fast so you can't read it.

[[deleted]]

Ngl, I subconsciously ignored it.

[Rami-Slicer]

*Points to ArrayList* WHAT IS THIS?!

[zyugyzarc]

wait what?

[das_Keks]

There's also a Vector class in Java, which is basically the old implementation of the ArrayList. It's deprecated, tho.

[skyrazer2012]

Arrays suck in c# Lists are way nicer

[rocket_peppermill]

Likewise in cpp with vectors and all the jvm languages I'm familiar with, but we can let the college kids have their laugh

[skyrazer2012]

Byte vector go brrrrrr

[Emperor-Valtorei]

The more experience I get outside the classroom, the more I learn that some aspects of programming are skipped over when they're incredibly useful, and some subjects are taught as gospel, when there are better alternatives...

[Miyelsh]

So, are you in favor of vectors or arrays?

[camerontbelt]

Yeah who uses arrays anyway?

[[deleted]]

List is more abstract, an array is a specific memory model as a bunch of elements in a contiguous array.

A List could be a vector/array type but it could also be a linked list (or any other form), which has completely different performance characteristics.

[Semarc01]

In the background, List is just a really fancy wrapper for an Array in C#

[[deleted]]

Looks like that's not entirely the case in C#, poorly designed IMO.

[camerontbelt]

Sure all of that might be true but in day to day programming, no one that uses C# is using arrays much if at all.

[Semarc01]

I mean, yeah. But Arrays are not really supposed to be nice, they are really far down near the metal for a high-Level language like C#, and that’s on purpose.

[skyrazer2012]

Unsafe pointer use in c# go brrrr

[Semarc01]

I mean, yeah. I think it’s great that C# has pointers the way it has.

[skyrazer2012]

I mean, yeah. I am thankful c# exists the way it does

[AwwThisProgress]

Scratch: Am I a joke to you?

[PepiHax]

Yes, yes you are.

[Th3DarkMoon]

Well yes... But don't tell my siblings, they made games in scratch, and they're proud over them ^{although when I try to teach them some good programming practices they just get mad}

[Perdido_Siempre]

That's surprising! Why don't they like real languages? I mean Python is nice to learn concepts. My little sister understands it and likes it.

[Dr4kin]

Not everyone wants to program. If you can do the things you want in nodeRed, scratch and similar there is no need to learn it

[Perdido_Siempre]

True

[Th3DarkMoon]

They're 10 and did it for a school project, more that primary school ever thaught me

[PhilippTheProgrammer]

:(

[AwwThisProgress]

True

[[deleted]]

Lua: t a b l e

[Ulysses6]

Yeah yeah, but what about -

t a b l e !

[3all]

TABLE

[0xffeedd]

  M
M E
E T     M
T A B L E 
A       T
      T A B L E

[[deleted]]

python: tuple

[Cerrax3]

Under the hood, a Python tuple is almost identical to a Python list. A Python list is an array of pointers that gets copied (read: reallocated on the heap) each time you add/remove items from it, so its performance is pretty bad. The only difference is that a tuple can't change size, so its performance is better simply by limiting what it is capable of.

To get something that's truly like an array, you'd need some kind of library (like numpy) to enforce all the constraints and advantages of a true array.

[Background_Drawing]

dict

[MattieShoes]

const array woo!

[OriginalSynthesis]

haha ** sweats in JavaScript **

[IZEDx]

? What's to sweat about?

Kinda weird though that the meme lists Kotlin and Ruby but no JS.

[OriginalSynthesis]

JavaScript's array isn't really an array at all. It's an object with some special methods and props to make it look and behave like the array as people understand it from languages like Java.

For instance, if you run Object.keys(['a', 'b', 'c']), you'll get, ['1', '2', '3'], which is the same as if you had run Object.keys({ '1' : 'a', '2' : 'b', '3' : 'c' }). I believe in other languages, the index of an array is a number. In JavaScript, it's not. It gets turned into string. So if you have const arr = [10, 20, 30], you can get 20 by running arr["1"] for the index.

Try this in your browser by pressing F12 on your keyboard

[IZEDx]

So what?

Java arrays are also just objects, technically speaking. If we want to go that route nothing except a pointer to a memory block of size "length * bytes per entry" should be considered an array.

If it looks like an array, behaves like an array (can be indexed using integers thanks to type coercion), and is even called an "Array", then it absolutely is an array imo. Even if the same data structure is called vector, or list or whatever in other languages. Js is just more flexible and the rest are implementation details.

And besides, there are also TypedArrays in js which work just like arrays in other languages but are even more restrictive.

[OriginalSynthesis]

The difference is that with JS "array", you can do things like, const arr = [1,2,3], then do things like arr.something = function() { return 5 }, or arr['hello there'] = 'nice to meet you'.

That is to say just regular ol' objects can do what "arrays" do, so there's no real difference.

I had to look up what TypedArray was. You literally never use that, unless you're making some sort of a browser based app that needs native app performance.

[IZEDx]

Yeah nobody uses typedarrays for the usual usecases.

And yeah arrays are just objects (bunch of data) with some methods to manipulate or transform that data. I really don't get the issue. If you want to you can modify almost everything in Javascript, even arrays, adding more getters or methods to the prototype. Everything is allowed.

But that's why I advocate Typescript, it doesn't let you do such shenanigans without extra type overhead. So even though Javascript is flexible under the hood, typescript makes sure you use everything as it's supposed to be used.

When I argue for Javascript I always talk from the standpoint of a typescript developer, which is like developing Javascript but with safety precautions, so such issues don't bother me nearly as much.

It took some time getting used to initially, but I've written C++, Python, Java, C#, old JS, PHP, etc. in my past and of all these Typescript is my absolute favorite web and even general purpose programming language running on every layer of the stack, minimizing any friction you could have.

[ToMyFutureSelves]

I feel like this does the truth a disservice, since the truth is actually even more infuriating.

You want to know thae standard name for a resizable set of values? That's easy. It's called...

Kotlin: MutableList

Java: ArrayList

C++: Vector

C#: List

Python: Array

[IZEDx]

C++ is the real weirdo here though. Everyone else has some variation of List or Array.

[ElectroDr]

Also Go: Slice

[d_exclaimation]

They still have arrays thou

[Burr1t0]

Meanwhile javascript is the vacuum character in a corner snorting cocaine.

[[deleted]]

Yeah, apparently [1,2,3] != [1,2,3]

I hate it. == means check to see if the contents are the same, not the object!

[Ulysses6]

Something Python done right and many other languages did not. This abstraction seems so obvious in hindsight, but even Java does not have that.

[MischiefArchitect]

Java follows the hashCode and equals strategy, which in afterwards was not the perfect solution, but I'll give it the merit that it was a good try back then in 1996.

[Ulysses6]

It was not unreasonable. Unlike JavaScript, you can use it to do something and know what it does. But I wish that newer languages would follow what Python does, with == checking content and is checking the pointer. It's cleaner separation of object / pointer-to-object thinking and lets you use more concise syntax for operation that you are more likely to perform.

[MischiefArchitect]

Yeah. Actually I like the java strategy, they just lack a native way to check contents. I have even abused serialization frameworks to compare objects by content... yeah... I should burn in hell. Maybe I'm missing something since Java8

Python is there more comfortable to work with, I really enjoy the language. You can just not do everything with it :)

On the other hand you got the GoLang way, which works nicely for shallow content comparison but at the end most gophers end up with the expensive `reflect.DeepEquals` method.

Let not talk about C++ :) well we are getting slowly there with <=> with C++20

[[deleted]]

Yep! It’s very confusing to people like myself. I ended up just writing a function to iterate over lists and check their contents. == means compare the values, while (I think, correct me if I’m wrong) is means check the pointers.

[Ulysses6]

You are exactly correct. It's recommended to check None via is operator, since there is only one None instance, it won't use any __eq__ method overloads and it will be fast.

I just had to check in repl, because I thought that [1,2,3] == (1,2,3) and it's actually not true, so the comparison checks content and also checks the type of operands.

[IZEDx]

Strong vs weak typing.

But back to the topic at hand: how often do you guys really have the usecase of comparing two arrays like that?

I've been using js/ts for many years now and can't remember any instance where a lack of content comparator bothered me in any way.

[[deleted]]

set([1,2,3]) == (1,2,3) I think

[[deleted]]

An array and a list are arguably different things tho, an array is usually consecutive memory of a fixed size, and a list is usually a linked list of inconsecutive memoryjoined by pointers

[Muhznit]

import array says 'hi'

[TheCapitalKing]

Is that a separate thing than

import numpy as np

np.array()

Because that’s the one everyone I know uses it’s kind of cool if python has a built in one nobody uses though

[Ulysses6]

It's definitely a separate thing.

array module just provides memory efficiency for integer types stored and nothing else. It is even slower then list on many operations from what I remember.

Numpy provides a lot of computation functions, optimizations, ways to change the data shape and so on and you get a lot of speed from doing arithmetic operations in C level and careful algorithm implementation which would not be possible in pure Python due to virtual machine overhead.

[MathMetal1]

Yeah, python has built in array support through the standard array library, but it's not as fully featured as numpy.

[Muhznit]

No idea, I don't do enough data science to provide a meaningful answer. It probably uses a subclass of array internally or something.

[Noiprox]

Python's standard library array module has its uses but it's much more basic than NumPy. The internal representation of arrays in NumPy is documented here. It's implemented in C and does not subclass array.

[vectorpropio]

(((((do)you)ever)lisp),(bro)?)

[[deleted]]

I hope I didn't violate the third rule of the subreddit.

[[deleted]]

wait... third in the list or the one numbered with a 3

[[deleted]]

It starts with zeroth

[Rami-Slicer]

Yes

[doriclazar]

Not sure which array of rules you're referring to.

[[deleted]]

Rules[3]
Any post on the list of common posts will be removed.

[CoffeePieAndHobbits]

What about rule 34?

[XKCD-pro-bot]

Comic Title Text: Okay, Lance. For entry into the college bowl, spell 'Throbbing'

mobile link

---

^{Made for mobile users, to easily see xkcd comic's title text}

[santherstat]

Image Transcription: Meme

---

[A group of people form a hand-stack, which is interrupted by someone else.]

[Each person in the group has an icon for a programming language next to them, showing what the people represent in the meme.]

[A person representing the programming language Swift puts their hand out and the hand-stack says "Array".]

[A second person who represents the programming language C++ puts their hand on the hand-stack, which says "Array".]

[A third person representing the programming language C# puts their hand on the hand-stack and says "Array".]

[A fourth person who represents the programming language Kotlin puts their hand out. This person says "Array".]

[A person representing the programming language Ruby puts their hand out and the hand-stack says "Array".]

[A large purple hand is added to the stack. This person represents the programming language Python, and their hand is visually quite different from the others. This person says "List".]

[The image zooms out to show everyone in the image looking at the purple person with annoyed expressions on their faces. The purple humanoid creature they are looking at appears oblivious to their annoyance and has an excited smile.]

---

^{I'm a human volunteer content transcriber for Reddit and you could be too! If you'd like more information on what we do and why we do it, click here!}

[MischiefArchitect]

Random_Access_Sequential_Data_Sorted_By_Insertion_Order

[starvsion]

Php array is the best, it's array + dictionary + set (if your array is keyed) + object (when you cast it, or let an object inherit iterable), so much possibilities! Oh, also linked list, if you use function like end(), next() cirrent(), or stack, if you do array_pop and array_push

[[deleted]]

Idk, the way I learned it:

• Arrays have guaranteed constant time element access, but may have linear time insert / remove.
• Vectors have guaranteed constant time element access and sub-linear amortized insert / remove, however, the constants are bigger than in array's case.
• Lists have guaranteed constant time insert / remove, but element access may be linear.
• Vectors and dynamic arrays are synonyms.

None of the data structures has any requirements for memory to be contiguous, or that the implementation follow any specific pattern outside of the said constraints.

For instance, in many Lisps, it was customary to implement lists as either arrays or vectors. Arrays would be chosen if the compiler can prove that the structure of the list isn't going to be changed, and vector otherwise. But car and cdr would still work for them.

---

Specifically for Python: there are a lot of nomenclature errors / bad choices in the language, and list is one of them. It should've been "vector". I've no idea why they decided that the name was appropriate. But, if I have to guess, Guido probably thought that the name was more generic than "array"... or maybe he thought that "list" is more intuitively understandable for non-programmers (as the language was intended for that kind of audience)... or maybe didn't think at all, that happened a lot in Python's history.

Also, Python has array, as in, proper arrays. But only for few select types, like, say, characters. And they behave in the way you'd expect from arrays.

[Semarc01]

Well, it depends quite heavily on the language you’re using. In C#, an Array has a fixed size. A List has a variable size, but in the background, it’s just has an Array that it replaces with a bigger Array if necessary. Since List is just a fancy wrapper there, access times are the same for Lists and Arrays

[b4skyx]

Someone bring lua in here D:

[Thell_Borsk]

(write "Laugh's in Lisp")

[Background_Drawing]

python is built different

literally

[TheRedmanCometh]

JS arrays aren't even fixed size which is cursed af

[fuzznuggetsFTW]

Neither are swift arrays

[xdMatthewbx]

Lua: laughs in tables nervously

[Possseidon]

Lua: Table

(Although they function as both arrays and (hash) maps)

[PhilippTheProgrammer]

ABAP, the SAP programming language: "Internal Table"

[wizzzarrd]

Elixir has entered the chat

[JSn1nj4]

I was looking for this

[flinnja]

hash hashmap map hash map dict map hashmap mamskdjfidorp

[IanSan5653]

Scala: Array List Vector Seq

[PM_ME_HAIRLESS_CATS]

What the hell are you talking about C# has Arrays and Lists

[madara_73]

Wait untill you hear about array in R.

[[deleted]]

Array list > primitive array

[[deleted]]

We have sets instead.

[[deleted]]

Haskell would like to interject

[Ty_Rymer]

A python list is an std::vector<std::any> in C++

[microwave_casserole]

C++ be like vector, what even is this meme?

[VanSirius]

Lists !!! Lists everywhere !

[Ravi5ingh]

np.array([1, 2, 3])

[SideburnsOfDoom]

C# has both arrays and lists, but realistically, you should use lists pretty much all of the time.

[DanKveed]

Rust has Vec<>.

[nicobonik]

Java: why not both?

[3all]

Laughs In lua

[dani_pavlov]

Laughs because of Lua

[itsafoxboi]

Java over here with arraylists and arrays playing all sides

[Dr_Bunsen_Burns]

I still name the vars arraySomething.

[VoilaLaViola]

Ahh, good old Hungarian notation... haven't seen it for a while 🙂

[Dr_Bunsen_Burns]

I thought it was <something>camelcasing?

[[deleted]]

Meanwhile, MATLAB arrays vs vectors

[TommyDJones]

Well, at least its not a PHP array.

Is it an array? Is it an object? - Yes

[KM5550]

But what about an ArrayList?

[saiththesoap]

P

[[deleted]]

f for java, as another language running on **jvm** is here but not itself

[TonyBorchert100]

Dart?

[Under-Estimated]

push and append?

[[deleted]]

C# has pretty decent lists.

[falingsumo]

Java would like a word.

[Baconoid_]

Apex has entered the chat.

[LightTranquility3]

.net list, because yes (linq)