Can PyYAML dump dict items in non-alphabetical order?

Question

I\'m using yaml.dump to output a dict. It prints out each item in alphabetical order based on the key.

>>> d = {\"z\":0,\"y\":0,\"x\":         


        

Answer 1

There are two things you need to do to get this as you want:

• you need to use something else than a dict, because it doesn't keep the items ordered
• you need to dump that alternative in the appropriate way.¹

import sys
import ruamel.yaml
from ruamel.yaml.comments import CommentedMap

d = CommentedMap()
d['z'] = 0
d['y'] = 0
d['x'] = 0

ruamel.yaml.round_trip_dump(d, sys.stdout)

output:

z: 0
y: 0
x: 0

---

¹ _{This was done using ruamel.yaml a YAML 1.2 parser, of which I am the author.}

Answer 2

Building on @orodbhen's answer:

old_sorted = __builtins__['sorted']
__builtins__['sorted'] = lambda x: x
with open(filename, 'w') as outfile:
    yaml.dump(f_json, outfile)
__builtins['sorted'] = old_sorted

Just replace the built-in function sorted by a lambda identity function while you use yaml.dump.

Answer 3

If you upgrade PyYAML to 5.1 version, now, it supports dump without sorting the keys like this:

yaml.dump(data, sort_keys=False)

As shown in help(yaml.Dumper), sort_keys defaults to True:

Dumper(stream, default_style=None, default_flow_style=False,
  canonical=None, indent=None, width=None, allow_unicode=None,
  line_break=None, encoding=None, explicit_start=None, explicit_end=None,
  version=None, tags=None, sort_keys=True)

(These are passed as kwargs to yaml.dump)

Answer 4

One-liner to rule them all:

yaml.add_representer(dict, lambda self, data: yaml.representer.SafeRepresenter.represent_dict(self, data.items()))

That's it. Finally. After all those years and hours, the mighty represent_dict has been defeated by giving it the dict.items() instead of just dict

Here is how it works:

This is the relevant PyYaml source code:

    if hasattr(mapping, 'items'):
        mapping = list(mapping.items())
        try:
            mapping = sorted(mapping)
        except TypeError:
            pass
    for item_key, item_value in mapping:

To prevent the sorting we just need some Iterable[Pair] object that does not have .items().

dict_items is a perfect candidate for this.

Here is how to do this without affecting the global state of the yaml module:

#Using a custom Dumper class to prevent changing the global state
class CustomDumper(yaml.Dumper):
    #Super neat hack to preserve the mapping key order. See https://stackoverflow.com/a/52621703/1497385
    def represent_dict_preserve_order(self, data):
        return self.represent_dict(data.items())    

CustomDumper.add_representer(dict, CustomDumper.represent_dict_preserve_order)

return yaml.dump(component_dict, Dumper=CustomDumper)