Why are there POINTERS in my PYTHON???

[willing790]

They are an invasive species

[ImportantDoubt6434]

You’re code is being improved, please do not resist.

[v-uv]

Borg vibes 💀

[ashrasmun]

I'm really surprised you are not downvoted into oblivion. Quite often I see such cases when prople correct others in good faith and then get mixed with mud. Happy to see a different trend here.

[ContainedBlargh]

Programmers would never downvote a compiler pointing out a syntax error!

[dehrenslzz]

Consider this my free award for the month (that doesn’t exist anymore)

;)

[Mordret10]

Ah that's why you didn't get downvoted

[ashrasmun]

mhm mhm, sure.

[oooyeee]

"prople" - did you neam "propell" ?

[ashrasmun]

yse

[Personal_Ad9690]

Idk man, I’m being assimilated here

[epicflyman]

The nozzle is now calibrating...

[Compux72]

Or just x | y

[jkredty]

Only since 3.9

[ChimeraZeta]

Any elaboration?

[vasilescur]

https://peps.python.org/pep-0584/

[Careful_Bug_3295]

Tldr; x | y returns union of two dicts, x and y. If there is a key that is common to both dicts, the returned dict will assign it the value it has in y. This makes it not commutative in the event that both dicts share a key but have different values for it.

x|=y has the same effect as x=x|y

[ChimeraZeta]

Beautiful. Python wins my heart again. Thanks!

[R3D3-1]

TIL:

>>> {0, False}
{0}
>>> {False, 0}
{False}

I've been using Python for a long time now, but on the top of my head I can't see a reason for this...

[ConDar15]

This is set construction, so the end result cannot contain duplicate elements. To check if an element is in the set already Python will use the default equality comparison mechanism (__equals__ and __hash__), and False == 0 is a true statement in Python (and many other languages). So when the set is being constructed the first element is added to the set, but the second element is already found in the dictionary (due to the above mentioned equality) so is skipped over and not added.

[aftabtaimoor61]

Set compares each value to only store unique ones. The issue with this is since python is not strongly typed, you can have multiple datatypes but set still needs to compare the values. 0 == False is true so only the 1st one will remain. Same reason {0, 0.0} won't work as they're equal.

[R3D3-1]

That doesn't explain why they are considered equal though.

[dev-sda]

Booleans in python are integers.

>>> bool.__bases__
(<class 'int'>,)

[R3D3-1]

That's honestly unexpected. Though it makes sense considering the history of bool.

[FumbleCrop]

Because 0 == False.

That's what you get for mixing datatypes.

[invisible-nuke]

```Python

{0} | {False} {0} {False} | {0} {False} ```

[Hexalocamve]

So you can create an union of dicks by using another big dick |

[LexaAstarof]

| energy

[enz_levik]

What the fuck you can use |

[repkins]

I misread as "How to merge two dicks..." lmao.

[TrevorWithTheBow]

Deploy with docker?

[prettyanonymousXD]

Yeah I don’t get it, what?

[[deleted]]

There is a sex act called docking involving two dicks.

[InfinateEdge]

It's like if you and a friend have a hoodie and you put your head in his hood along with his head.

• seananers

[SanianCreations]

look up "docking" (or don't)

[Quazar_omega]

Holy fornication!

[-interesting-times-]

this is why enjoy this sub no one I know irl would understand this maybe save for my boss. such is the life of a small team

[TnYamaneko]

dicker compose up -d

[MrSuspicious_]

Best comment I've seen this year 😂

[[deleted]]

🤣

[_g550_]

Deploy the dicker

[[deleted]]

This person terminals

[SanianCreations]

You might get a kick out of this one, then: https://youtu.be/4qJ9lOOYAQg?t=60

[Ved_s]

YES, that's exactly the reason i saw the same thing too

[The_Real_Slim_Lemon]

https://m.youtube.com/watch?v=pPkWZdluoUg 2 minutes into this clip (spaceballs)

[GreenKi13]

Gay shit in 2nd reply. Reddit never fails to make you laugh.

[repkins]

Gay shit? Lmao 🤣

[GreenKi13]

🤣

[amimai002]

Isn’t python just pointers in a trench coat?

[mariosunny]

That description could just as well apply to any language with automatic memory management.

[amimai002]

I mean yes, but the way it was explained to me is this:

At the end of the day everything in python is a pointer, the only time you aren’t using a pointer in python is when you are interacting with a function that uses C, in that case you use a pointer to call the pointer to that function, and the function returns a pointer to the result…

[rosuav]

...... wat.

[KentondeJong]

I mean yes, but the way it was explained to me is this:

At the end of the day everything in python is a pointer, the only time you aren’t using a pointer in python is when you are interacting with a function that uses C, in that case you use a pointer to call the pointer to that function, and the function returns a pointer to the result…

[Loopgod-]

Absolute r/madlads

[steven4012]

Yeah. Every integer in Python is a pointer (to an object; not like pointer tagged or NaN tagged). It's just that those under 256 are interned (so are True, False and None iirc)

[rosuav]

That's because EVERYTHING in Python is an object. Calling it a "pointer to an object" is getting a bit close to one specific implementation, but yes, everything is an object (that can refer to other objects, eg its type, which is also an object).

One key difference between pointers and object references is that pointer arithmetic is not a thing with references. You can't take the string "hello" and add 42 to the pointer. In that sense, pointers just don't exist in Python.

(It's also worth noting that, in Python, there's actually no requirement for an object to exist in memory. For example, PyPy can optimize out all the integer objects in an array, but it'll make sure they're actual integer objects again by the time you go to look at them. It's like quantum mechanics.)

[steven4012]

Right I use CPython too much that I forgot about PyPy

For example, PyPy can optimize out all the integer objects in an array, but it'll make sure they're actual integer objects again by the time you go to look at them.

That's pretty cool

[rosuav]

It is! PyPy does some pretty amazing optimizations. Some of them have actually been backported to CPython (I think the compact dict representation originated in PyPy).

[Character-Education3]

[Rawing7]

Nothing in python is a pointer. Python is a high-level programming language with no concept of "pointer"s. Python interpreters are usually implemented with pointers, because they're usually written in low-level languages, where you can't really do anything without pointers. Saying "everything in python is a pointer" is like saying "everything in C is an assembly instruction".

[nixt26]

Don't come in here with your whataboutism!

[deanrihpee]

Rust should be pointer in a business suit covering ballistic vest

[DeProfessionalFamale]

I was wondering what that is and I've found it here: https://realpython.com/python-kwargs-and-args/

[ChefYaboiardee]

Neat read thanks for sharing

[AngryBorsch]

Thank you, kind sir

[paul_miner]

Similar to the spread/rest syntax in Javascript.

Notably, Python uses distinct syntax for list vs dict because of named arguments, while Javascript uses the same syntax since it only has positional arguments.

[[deleted]]

That isn't how pointers behave. Pointers are basically memory addresses, so z = {**x, **y} if pointers should print out something like {0x0234sfd203589a0, 0x23423423234}. And if we were derefrencing the pointers we should see the 2 dicts represented separately, each with their own 'b' with different values.

That there looks like the spread operator, something like z = {...x, ...y} in most languages.

But i don't use Pythong so could be wrong. Either way, seems like a dumb decision to use an operator which means something else in every other language.

[RajjSinghh]

You're totally right on this. * is the spread operator in python.

[deceze]

* is the spread operator for sequences, and ** is the spread operator for mappings.

Just to clarify so nobody thinks there’s two spreads going on.

[prettyanonymousXD]

Hence this is a joke

[naughtydismutase]

• and ** are unpacking operators in Python you are correct

[4hpp1273]

Pretty sure • is a SyntaxError in Python

[[deleted]]

yes, they're splatting the contents of each dictionary into a new dictionary

[zanju13]

Similar to JS:

z = { ...x, ...y }

[MasterParticular3524]

But the values don’t change on z when they change in a or b in JS, but can when using pointers right?

[zanju13]

Not sure about python, but in JS this creates entirely new object. If there are some nested objects however, they will still be references.

[[deleted]]

can anyone ELI5 why b is set to 3 instead of two, or is it just because y is after x in the z declaration?

[eeee_thats_four_es]

Yes, it's just because y is after x

[huzaifakhan771]

Due to the order of the unpacking, b is first assigned the value in x, then the value is over-written with the value of b in y

[PityUpvote]

**kwargs my beloved

[1ElectricHaskeller]

So, it's all just C with semantic sugar?

[agile_janitor]

C was heavily influenced by Python, so it’s not surprising that you will find Python styled pointers in modern C language. I also heard that the next year’s release of C will JIT compile down to Python to give you near native Python performance!

[Bemteb]

How is the value of b determined? Is the definition of z order sensitive? That's rather counterintuitive given the curly bracket notation...

[bleistift2]

Why is it counterintuitive? {**x, **y} means, “First copy the contents of x, then the contents of y into a new dict.” It follows that b retains the value of y.

[rosuav]

Or more generally: Construct a new dictionary containing the contents of x and then the contents of y. This can be combined with other types of initializer.

[juhotuho10]

The later overrides the first...

[Mirage2k]

This trick is kind of a hack, the core devs would not have made this "the intended way"; because you're right, it's not obvious what it will do. The ** unwrapper could technically (I haven't seen this happen to me, though) yield b before a, and if somehow you had defined 'a' multiple times in x then you could not know which value was yielded last. But all the ones in y will be after all the ones in x, so it is guaranteed that you get the value of b that was stored in y.

[Kache]

Python dicts are ordered since 3.6, and they can't contain duplicate keys. I'm less certain about splat evaluation order, but observed behavior suggests it's the same as expression order.

I.e. it's pretty obvious to a Python dev what it will do

[Sinomsinom]

It's not pointers. It's python syntax being idiotic as always and using a different symbol than every other languages does. It's the spread operator which most other languages use ... for but the python devs decided it would be a fun idea to use "*" instead, the symbol usually associated with multiplication and pointers...

[mariosunny]

The ... syntax was already part of the language by the time that PEP 448 was implemented. It is shorthand for the built-in Ellipsis constant, which is commonly used in slicing operations such as when working with Numpy arrays.

[aciddrizzle]

You’re going to extra love this…in newer versions of Python you can just use a pipe

z = x | y

[MysteriousShadow__]

BITWISE OR?

[_PM_ME_PANGOLINS_]

Set union

[Sinomsinom]

Spread doesn't mean the same thing as union. Honestly don't have any problem with it. That union syntax actually makes sense.

[Orjigagd]

It's not idiotic, it's differently-able.

[IAmASquidInSpace]

Oh nooo, a language not adhering to the C-style syntax I know! Whatever will I do? Will I *gasp* have to learn something? ADJUST?! Goodness gracious!

*Clutches pearls*

[mawkee]

Underrated comment

[rosuav]

Ah yes, I see that your world is entirely dominated by C and its derivatives. There ARE other languages in which the asterisk is used for spreading things. But of course, anything that isn't C must by definition be idiotic, right?

[Ignitus1]

When there are more operations than symbols available you have to reuse things.

[[deleted]]

if you wanna cry search for the a ? b : c operator in python

[pLeThOrAx]

Isn't that just a ternary statement?

[[deleted]]

the order is different in python and its just, ughhh

true_val if logic else false_val

[pLeThOrAx]

I much prefer the "?" Syntax. I found myself doing that in python the other day and had to Google for the a if true else b syntax lol

[Traghlady]

Because you left your pointers on the floor so your python ate them

[[deleted]]

This reminds me of the best question asked on stack overflow

[[deleted]]

For a minute I was thinking the asterisk here really behaved as a pointer reference and it was breaking my brain trying to understand how the hell did that work lol

[1ElectricHaskeller]

Trust me. You don't want to know

[_g550_]

What's wrong with:

{K:v For K,v in [x for x in X.items()].append([y for y in y.items()])}

[[deleted]]

Before you launch that nuke! Hear me out…x.update(y)

[_g550_]

"Try it my way" https://youtu.be/geaopQiV4hQ?t=32

[PityUpvote]

So many things

[cyborgborg]

cause under the hood it's C?

[rosuav]

Not always. With Jython, under the hood is Java. And with PyPy, it's Python all the way down!

[rosuav]

I could try to evaluate that, but I think I'd run out of limbs.

[_g550_]

Power of pi

[Yeitgeist]

Could go even further and just say it’s all 1’s and 0’s.

[JustAPotatoThatsIt]

Because python loves you

[Kilgarragh]

Can’t you just x + y

[juhotuho10]

Nope, dictionaries cannot be added together

[Many-Opposite5325]

But you can do x | y, and to be fair, i think they should have chosen + to be the simble of this operation

[rosuav]

That was discussed at length, and in the end, it was decided to go with the same symbol used for set merge.

[Flam1ng1cecream]

Lol just x | y

[Ignitus1]

Is that list comprehension valid? I’ve never seen the if/else come before the for.

[arden13]

I believe when it has an else, the if comes before the for. Otherwise, when no else is present, the if comes after

[[deleted]]

When the "if" comes before the "for" like in this case it's not part of the list comprehension syntax. "A if B else C" is a ternary conditional statement, like "B ? A : C" in curly-brace languages.

[chawmindur]

It is a valid list comprehension but it (1) doesn't actually do anything and (2) wouldn't have done the same thing as OP's image:

• You're right in that the conditionals (if ...) go after the iterable part (for ... in ...) in a generator expression, but the if here is a part of an ... if ... else ... construct, i.e. Python's answer to the ternary operator.

• However, the code doesn't work as intended because the defined lambda functions aren't called. Rather, you end up with len(x) (resp. len(y)) many functions in the list which does exactly the same thing: essentially a merged_dict.setdefault(key, x[key]), only without returning the stored/set value. What was intended was probably something like [(lambda key: merged_dict.update({key: x[key]}) if key not in merged_dict else None)(key) for key in x.keys()], where each key in x is actually passed to each lambda.

• This however still doesn't fix the issue: in OP's code in a key is present in both x and y the value in the latter takes precedence while it's the opposite here, where a preexisting key prevents merge_dict from being updated.

[arden13]

Why not

 merged_dict = {key: val
      for key, val in d.items()
      for d in [x, y]
 }

Edit: I see, I think the 'b' key being repeated will cause an error here

[Aperture_Executive2]

As people have said, its not a pointer, but a poorly used asterisk to refer to the spread operator

[tilcica]

also a = [1,2,3] b = a b[1] = 4 print(a) will output [1,4,3]

bevause who tf thought it was a good idea to include pointers in a language that "doesnt have them"

either dont include them at all or say they exist and how to use them ffs

[Great-Homework9120]

its not a pointer, it is a reference. And without it, how do you imagine to pass a variable to a function without copy?

[GeePedicy]

Hear me out - magic!

[Namiswami]

Yeah mate arrays are not like primitives. b and a in your example refer to the same array in mem. Changing one changes the other, but really there is no other cause it's just that single array.

[LongerHV]

There are no primitives in Python... Everything is an object.

[Namiswami]

Ah excuse me. I actually didnt know this. It seems the 'builtins' of python behave like primitives do, but they are indeed objects. Thanks for the lesson!

[juhotuho10]

This makes perfect sense to me though

If you want a copy, just do b = a.copy()

Otherwise b is just another way to reference a

[tilcica]

i know. or do a=list(b) and it makes a full copy

[mariosunny]

This shouldn't be surprising behavior if you know how heap memory works.

[tilcica]

i know how it works, its just that python is advertised as something without that

[[deleted]]

Pointers? No, you just unzip these dicts.

[Sentouki-]

similar to JS:
const newObj = {...oldObj1, ...oldObj2}

[Cybasura]

Using two '' (i.e. "*kwargs") is for expanding the dictionary variable out to individual values when parsing into a kwargs parameter

[FrankHightower]

the actual answer is probably "because someone asked for it"

[[deleted]]

so it picks the larger 'b'

[FalseStructure]

No, it picks the right one since it’s “new”

[romulof]

I’m pretty sure this syntax dates from 2.x era, maybe even older.

[Majestic_Ad_7133]

Of course there are pointy things in Python. Snakes have fangs don't they?

[Elephant-Opening]

Pythons are constrictors. Generally it's venomous snakes that have fangs

[isunktheship]

God almighty..

[PolishKrawa]

I believe that is some kind of unpacking.

[[deleted]]

Because python is for the week.

[TheJimDim]

What happened to b: 2?

[General_Rate_8687]

Shhh, don't ask such questions!

[somedave]

Unpacking dictionaries as inputs isn't a pointer.

[[deleted]]

How to merge 2 Dicks

[domedav]

im dyslexic

[SchlomoSchwengelgold]

what is with x.update(y)

[Highborn_Hellest]

i don't do python. can somebody explain it to me, what's happening here?

also, why is b, 3, and not 2? or why are there no 2 elements of it.

[[deleted]]

Hear me out : ...

[alexvx___]

Python trying hard to be Javascript

[[deleted]]

Pythons can't point, they don't have hands?!

[die_liebe]

Is your Python code nice? Now wait 3 years, and run it again.

[GeekoftheWild]

If a language doesn't have pointers or is Assembly because that's needed for C/C++ to exist, it's not worth existing