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Python dicts are now ordered

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Re: Python dicts are now ordered

#301

Post by dpacmittal »

tylerjwilk00 wrote: post #297
skrebbel wrote: post #242

Earlier quoted context omitted.

Sure, PHP arrays are actually ordered maps, but it's super confusing when used as arrays. I mean, look at code like this: $arr = []; $arr[2] = "two"; $arr[0] = "zero"; $arr[1] = "one"; echo join($arr, ", "); // two, zero, one In any other language, the result of similar code would be "zero, one, two". You'd need to `ksort` this thing to get it to behave like a normal bog-standard boring array. Everybody's writing PHP…

I have to disagree also. The order inserted makes most sense in most cases. Hand crafting integer based array indexes out of order is rare. And as you say a simple ksort call guarantees sort order. ksort($arr); echo join($arr, ", "); // one, two, three

Exactly. Of you hand craft an array you probably need it in that order.

Re: Python dicts are now ordered

#302

Post by ivalm »

tene wrote: post #298
skrebbel wrote: post #223

This is awesome, because the ordered map is the best data structure out there for easy & predictable programming, possibly only barring the array. There's so many cases where it's a benefit for map entries to retain order (and none where it's a problem). PHP really got this one right (and immediately messed it up by mixing ordered maps with arrays into a big soup, but hey, PHP). And so did, JS, sorta-kinda-by-acciden…

Could you explain some examples of what this is useful for? What sort of algorithms or operations do you have in mind where you both want insertion order, and also key-based lookup in the same data structure? I've made heavy use of all kinds of maps, and of queues and channels and arrays, but I don't recall ever noticing a situation where I wanted the properties of both mixed into the same data structure. I'd love to…

I think there is a lot of counters you might want both.

For example, supposed you have a list of ids accessing some system, you may want to count the raw number, but then also have some transformations thereof that are still ordered by count.

Example

  l = getListOfAccessIds()
  counts = Counter(l)
  total = np.sum(counts.values())
  fractions = {k:v/total for k,v in  counts.most_common()}

  #use the fact new dictionary is still ordered by most common
  plt.semilogy(fractions.values())
  plt.plot(np.cumsum(fractions.values()))

  #still works like dict
  print(fractions[id_of_interest])

Re: Python dicts are now ordered

#303

Post by squeaky-clean »

BiteCode_dev wrote: post #266
rplnt wrote: post #251

Earlier quoted context omitted.

> about a feature we had since Python 3.6, in 2016 No, you had that feature in one implementation. Now it's in the language specification. That's vastly different because only now you can rely on it without fearing it can go away with the next release.

First, cPython is 99% of Python deployments. So much that if a script works on it but not on another implementation, people often consider the later broken. As this post proves that most people don't even know about this feature, you can be pretty sure the vast majority of people don't know about pypy, micropython, etc. Secondly, even if you want to nit pick, Python 3.7 made it official more than one year ago. We are…

There's also the indication that this is official, and not just an implementation quirk. I still used OrderedDict in 3.6 because there was no guarantee 3.7 (or later) wouldn't silently break ordering on the standard dict. At least now it's unlikely to change because it will be considered a breaking change.

Re: Python dicts are now ordered

#304

Post by thedirt0115 »

masklinn wrote: post #280
jmilloy wrote: post #212

Earlier quoted context omitted.

I might have preferred odict be added and dict left alone, so that you didn't have to import OrderedDict when really you just want the new dict. If dict and odict mapped to the same thing for a while, fine, but dict could diverge again if desired.

The problem is that when you behave a certain predictable and deterministic way users will leverage that even if it's not specified. That is actually why the Python maintainers decided to make this behaviour official: the ordering was the consequence of changes in implementation details, but over 3.6's lifecycle they feared it would cause compatibility issues as users would start relying on the ordering properties of…

"users will leverage that even if it's not specified" -- reminds me of the classic xkcd, "Workflow": https://xkcd.com/1172

Re: Python dicts are now ordered

#305

Post by hprotagonist »

fock wrote: post #256
hprotagonist wrote: post #175

Earlier quoted context omitted.

tensorflow didn't work on 3.7 for a solid 8 months because some people at google very unwisely decided that `async` and `await` were great choices for variable names, despite PEP492 landing in 2015.

that's because tensorflow is advertisement for Google and while it's technically open-source, it doesn't stand for any kind of community-project, it's all there to show off (and ingrain in its users) the way Google wants things to Go (just look at the byzantine Bazel-build-processes - tensorflow taking hours to build and pytorch about 10minutes...).

my torch builds also take hours.

facebook is just as capable of writing hot garbage, sadly.

Re: Python dicts are now ordered

#306

Post by cliffy »

kingdomcome50 wrote: post #278
skrebbel wrote: post #242

Earlier quoted context omitted.

Sure, PHP arrays are actually ordered maps, but it's super confusing when used as arrays. I mean, look at code like this: $arr = []; $arr[2] = "two"; $arr[0] = "zero"; $arr[1] = "one"; echo join($arr, ", "); // two, zero, one In any other language, the result of similar code would be "zero, one, two". You'd need to `ksort` this thing to get it to behave like a normal bog-standard boring array. Everybody's writing PHP…

I disagree. The behavior you exhibit makes more sense than the behavior you imagine. You start with an _empty_ array, then (somehow) set the third element of that array? That makes very little sense. Had you _initialized_ your example as an array with a length of 3, your desired behavior would, indeed, manifest.

The problem is PHP calling an ordered map an array. Array in pretty much every other language means a sequence indexed by integers.

Ideally the maintainers of PHP would rename it and deprecate the use of `array()` over a long period of time.

Re: Python dicts are now ordered

#307

Post by behindsight »

tene wrote: post #298
skrebbel wrote: post #223

This is awesome, because the ordered map is the best data structure out there for easy & predictable programming, possibly only barring the array. There's so many cases where it's a benefit for map entries to retain order (and none where it's a problem). PHP really got this one right (and immediately messed it up by mixing ordered maps with arrays into a big soup, but hey, PHP). And so did, JS, sorta-kinda-by-acciden…

Could you explain some examples of what this is useful for? What sort of algorithms or operations do you have in mind where you both want insertion order, and also key-based lookup in the same data structure? I've made heavy use of all kinds of maps, and of queues and channels and arrays, but I don't recall ever noticing a situation where I wanted the properties of both mixed into the same data structure. I'd love to…

I use ordered maps to keep track of state snapshots/patches of redux/mobx-state-tree stores.

It allows me to both apply them sequentially as generated, or to "jump to" a particular point in time.

Re: Python dicts are now ordered

#308

Post by mehrdadn »

tene wrote: post #298
skrebbel wrote: post #223

This is awesome, because the ordered map is the best data structure out there for easy & predictable programming, possibly only barring the array. There's so many cases where it's a benefit for map entries to retain order (and none where it's a problem). PHP really got this one right (and immediately messed it up by mixing ordered maps with arrays into a big soup, but hey, PHP). And so did, JS, sorta-kinda-by-acciden…

Could you explain some examples of what this is useful for? What sort of algorithms or operations do you have in mind where you both want insertion order, and also key-based lookup in the same data structure? I've made heavy use of all kinds of maps, and of queues and channels and arrays, but I don't recall ever noticing a situation where I wanted the properties of both mixed into the same data structure. I'd love to…

For "algorithms", I mean, some really do care about insertion order. Like idk, if you have a priority queue, then you generally want FIFO ordering when the priority is the same? It like a pretty obvious desire in most cases... imagine a thread scheduler or a packet scheduler or what have you.

But generally it's about determinism and avoiding loss of information, not just whether a particular algorithm needs it. For example, you'd want serialize(obj) and serialize(deserialize(serialize(obj))) to produce the same output, otherwise you e.g. might not be able to cache stuf. But for a data structure like a hashtable, it's pretty tough (not logically impossible, but rather pointlessly difficult) to make that happen without preserving insertion order.

As another example, it's incredibly handy for a user to see items in the order in which they were inserted. Like say you're parsing command-line arguments, and the command is ./foo --x=y --w. If the user sees {x: y, w: None} then that tells them w was passed after x. That can be extremely useful for debugging; e.g. maybe you expected the caller to specify w earlier, in a different context and for an entirely different reason. Seeing that it came afterward immediately tells you something is wrong. But when such information is lost it's harder to debug code.

Re: Python dicts are now ordered

#309

Post by tylerjwilk00 »

acomjean wrote: post #203
zackmorris wrote: post #93

I'm glad to see other languages finally catching up to PHP. I'm joking (kind of) but after a lot of years of doing this, I've begun de-prioritizing pure abstractions and favoring the way that humans tend to do things on their own. Technically this is along the lines of the worse-is-better philosophy. The single biggest cost in software development is friction. Performance, size, etc are all less important, because th…

For those that don't know PHP associated arrays are equivalent pythons dictionaries. They are implemented as an ordered map. https://www.php.net/manual/en/language.types.array.php Its pretty much the main data type used in php. Once you get used to it is pretty powerful for dynamic languages. They even have built in sorts: https://www.php.net/manual/en/array.sorting.php They are "simple arrays" that have numeric inde…

Your point got me thinking...

PHP arrays may have been one of the "killer features" that lead to it taking hold of the web. It's so frictionless, powerful, and you can bend them to your will with ease.

Re: Python dicts are now ordered

#310

Post by wruza »

tene wrote: post #298
skrebbel wrote: post #223

This is awesome, because the ordered map is the best data structure out there for easy & predictable programming, possibly only barring the array. There's so many cases where it's a benefit for map entries to retain order (and none where it's a problem). PHP really got this one right (and immediately messed it up by mixing ordered maps with arrays into a big soup, but hey, PHP). And so did, JS, sorta-kinda-by-acciden…

Could you explain some examples of what this is useful for? What sort of algorithms or operations do you have in mind where you both want insertion order, and also key-based lookup in the same data structure? I've made heavy use of all kinds of maps, and of queues and channels and arrays, but I don't recall ever noticing a situation where I wanted the properties of both mixed into the same data structure. I'd love to…

  console.log(object)

  {
    keys
    in
    headache
    less
    order
  }
I find this use case severely undervalued in this thread and have no idea why. It helps so much in logging and/or debugging.
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