Allow to turn off sorting keys in Dumper

[perlpunk]

See issue #110

This allows to do:

output = yaml.dump(data, sort_keys=False)

The default is True because of backwards compatibility.

This can be useful for python >= 3.7 to preserve key order. Also not sorting will probably be faster.

I didn't add a test because I'm not yet familiar with testing in python
and couldn't find out how the pyyaml test suite works.

Also i don't know where to document that.

[perlpunk]

Travis tests are failing. I need to find out how to run the tests locally. Any hints for a python beginner?

[perlpunk]

thanks @ingydotnet for python setup.py test
I pushed a fix for cyaml.py, tests are passing now for python > 2.6

[perlpunk]

I started to write a test for this. Will probably push it tomorrow

[perlpunk]

rebased to master, tests now including 3.7-dev, and 2.6 is passing

[perlpunk]

Rebased to current master, squashed commits.
Tests are passing (and now include the libyaml tests also)

[dsposito]

This is great! Looking forward to this being merged! 🚀

[jasonrhaas]

Any progress on this PR?

[dsposito]

@jasonrhaas I'm hoping this eventually gets merged to source but for now oyaml does the trick.

[Ark-kun]

Please, merge this. I've spent countless hours trying to work around this.
P.S. No, oyaml is not a solution for us, since our team is already using pyyaml and does not want to change all code files.
P.P.S. No, OrderedDict is not a solution, because it radically changes the output and yaml types. (mapping to sequence)

[dilumr]

I too am interested is this. Would like to use in a feature where a tool slightly modifies YAML files that are checked into source. Would love the edits to look slight. The YAML files are initially ordered by hand, to expecting keys to be alphanumerically sorted is unrealistic; humans tend to group keys by purpose and/or importance.

[gatopeich]

Dear Perl punk (since you seem the only maintainer left here), leaving "sorted" by default is still wrong.

Sorting the keys is a superfluous operation wrt the YAML spec. It is also anti-pythonic, and goes against the most basic programming principle of not doing needless things.

Now it is obvious from the comments that devs using PyYAML for actual work are negatively impacted by this anti-feature. Like in my case, it renders this library unusable for their projects.

Whoever wants the keys sorted should be doing it at the .yaml source. That is the whole point of defining interfaces in YAML.

"Backwards compatibility" feels like a weak excuse here.

Please listen to the community and be honest here.

[perlpunk]

@gatopeich this is a pull request. It's a suggestion.

I don't decide anything, I can just help making decisions.

I agree that for python versions that keep the original order, sort_keys=False would be the better default.
For older versions I think that default wouldn't make sense, because getting an arbitrary sort order when dumping is less helpful than sorted keys. Plus it's not backwards compatible.

Would it make sense to make the default depend on the python version?
Thoughts?

[gatopeich]

Would it make sense to make the default depend on the python version?

Okay. Then let's apply same default as for json.dumps(): sort_keys=True until Python 2.6, False since v2.7.

[ofek]

Can this be merged now?

[rr-]

Would it make sense to make the default depend on the python version?
Thoughts?

If you're concerned about portability, it's okay to have it default to True. The important bit here is to be able to customize it at all, which we're still unable to.

(I think having a package changing its behavior after seemingly transparent Python upgrade breaks the principle of least astonishment, although personally I too would like to see it default to False.)

[perlpunk]

Closing, recreated based on current master: #254