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Python dicts are now ordered

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Re: Python dicts are now ordered

#171

Post by gnulinux »

rmdashrfstar wrote: post #155
gnulinux wrote: post #142

Earlier quoted context omitted.

Why does it matter if it's explicit or not. If python doesn't support forward compatibility, you should know that if you write code for 3.7, it's not gonna work in 3.5. Doesn't seem like a big deal to me.

Major version changes are for API compatibility. If there is a change which makes all other 3.* incompatible, then it should be a major version increase.

Who told you that? I'm looking at PEP 606, it says nothing like what you claim. https://www.python.org/dev/peps/pep-0606/

Re: Python dicts are now ordered

#172

Post by gmanley »

alayne wrote: post #164
_aleph2c_ wrote: post #144

This is an amazing contribution to the language. A mixture of speed and convenience, probably made by volunteers. As for people criticizing a change to what use to be a non-deterministic ordering of a dict iteration; I don't know what to say to them, other than, are you serious? There are people out there who are working for us, they work for free and they did some heavy lifting to give us this. They might read what…

Other languages don't generally have special order guarantees about standard maps. This seems very idiosyncratic.

I can't speak for all "other" languages but Ruby made the change years ago from 1.8 to 1.9. Ruby calls them hashes but they're standard maps. Obviously Ruby and Python are very similar but I think the point stands.

Re: Python dicts are now ordered

#173

Post by dekhn »

A bit of a side topic, but when Judge Alsup (himself a descendent of Boole and with a middle name of Haskell, and a programmer to boot) said "It is so ordered" (https://casetext.com/case/oracle-america-inc-v-google-8) in the Oracle Google case, I could only think that's what a computer scientist would say when quicksort was done.

Re: Python dicts are now ordered

#174

Post by dukoid »

alayne wrote: post #164
_aleph2c_ wrote: post #144

This is an amazing contribution to the language. A mixture of speed and convenience, probably made by volunteers. As for people criticizing a change to what use to be a non-deterministic ordering of a dict iteration; I don't know what to say to them, other than, are you serious? There are people out there who are working for us, they work for free and they did some heavy lifting to give us this. They might read what…

Other languages don't generally have special order guarantees about standard maps. This seems very idiosyncratic.

Java added LinkedHashMap a while ago. I tend to default to it except for small temporary use cases where order absolutely won't matter or have an outside impact...

Re: Python dicts are now ordered

#175

Post by hprotagonist »

abetlen wrote: post #91
jhrmnn wrote: post #57

Earlier quoted context omitted.

What you describe is forward compatibility, and Python (and most other programming language) doesn't have it.

TIL I suppose Python doesn't even have backwards compatibility within the same major release as we saw with the addition of the async keyword in Python3.5. Many older Python 3 packages broke because they expected that to be a legal identifier for a variable name.

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.

Re: Python dicts are now ordered

#176

Post by compiler-guy »

mark-r wrote: post #94
Sean1708 wrote: post #40

Earlier quoted context omitted.

My main issue with it is that if someone figures out an even better way to do dictionaries but it doesn't preserve insertion order, then that technique can't be used. But I certainly wouldn't call it a stupid decision, the problem is that once a behaviour is observable then people absolutely will start relying on it.

All they have to do is give it a different name, such as unordered_dict.

Which means no one gets it for free when it is added to the language.

Re: Python dicts are now ordered

#177

Post by zwp »

drngdds wrote: post #128
paulhodge wrote: post #60

Great decision IMO. I remember maintaining a bunch of Python code that we supported on both OSX and Windows. Out of all the platform-specific bugs we had (where it worked on one OS and not the other), one of the most common causes was code that relied on a certain key order. And we knew that relying on key order was bad, we're supposed to use things like OrderedDict, blah blah blah. It was still a really easy mistake…

I haven't done a ton of Python, but I can't really think of a situation where relying on a dict to be ordered is an easy mistake to make. Do you have an example?

I saw this in Perl a long time ago but it could just as easily have happened in Python. The dict (Perl hash) was a set of mappings for template replacement of "from" strings to "to" strings.

    "FOO" => "bar" # Replace FOO with bar
The author had considered the case where one key (FOO) might be a left-substring of another (FOOBAR), and so reversed the output from keys() before iterating over the hash. This ensured that FOOBAR, which sorts later, would be substituted before FOO (else FOOBAR -> barBAR, oops).

Unfortunately, despite empirical evidence to the contrary at the time, keys() does not guarantee sort-order results https://perldoc.perl.org/functions/keys.html

This worked for a while (appeared to work?) and but was subsequently caught by another developer, who added a sort().

(Get a templating library alreay yeesh).

Incidentally Ruby made the transition to sorted Hash some years ago (1.9 maybe?) and I don't remember any great fall-out.

Re: Python dicts are now ordered

#178

Post by lapink »

bbrik wrote: post #158
_aleph2c_ wrote: post #144

This is an amazing contribution to the language. A mixture of speed and convenience, probably made by volunteers. As for people criticizing a change to what use to be a non-deterministic ordering of a dict iteration; I don't know what to say to them, other than, are you serious? There are people out there who are working for us, they work for free and they did some heavy lifting to give us this. They might read what…

As far as I know, it was implemented by Raymond Hettinger. This is a very interesting talk about the new tech: https://www.youtube.com/watch?v=p33CVV29OG8&t=1202s

Indeed, here is the mail from Raymond Hettinger explaining the new design on the python-dev list: https://mail.python.org/pipermail/python-dev/2012-December/1... Quite amazing that it is faster, more memory efficient and convenient for the end user.

Re: Python dicts are now ordered

#179

Post by andrewshadura »

alayne wrote: post #164
_aleph2c_ wrote: post #144

This is an amazing contribution to the language. A mixture of speed and convenience, probably made by volunteers. As for people criticizing a change to what use to be a non-deterministic ordering of a dict iteration; I don't know what to say to them, other than, are you serious? There are people out there who are working for us, they work for free and they did some heavy lifting to give us this. They might read what…

Other languages don't generally have special order guarantees about standard maps. This seems very idiosyncratic.

Tcl's dicts are ordered.

Re: Python dicts are now ordered

#180

Post by pimlottc »

alayne wrote: post #164
_aleph2c_ wrote: post #144

This is an amazing contribution to the language. A mixture of speed and convenience, probably made by volunteers. As for people criticizing a change to what use to be a non-deterministic ordering of a dict iteration; I don't know what to say to them, other than, are you serious? There are people out there who are working for us, they work for free and they did some heavy lifting to give us this. They might read what…

Other languages don't generally have special order guarantees about standard maps. This seems very idiosyncratic.

For almost all intents and purposes, object keys have been ordered in JavaScript since ES2015. Map has always been ordered.

https://www.stefanjudis.com/today-i-learned/property-order-i...

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