maintain key order in pyyaml for python 2.7+

main.py

import yaml
from collections import OrderedDict 
                                    
class OrderedDumper(yaml.SafeDumper):                   
        pass
                              
def _dict_representer(dumper, data):                   
        return dumper.represent_mapping(
                yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
                data.items())
                   
OrderedDumper.add_representer(OrderedDict, _dict_representer)
                     
class OrderedLoader(yaml.SafeLoader):
        pass                    
                           
def construct_mapping(loader, node):
        loader.flatten_mapping(node)
        return OrderedDict(loader.construct_pairs(node))
           
OrderedLoader.add_constructor(
        yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
        construct_mapping)   
original = OrderedDict([
        ('one', 1),    
        ('two', 2),                    
        ('three', 3),
        ('four', 4),
        ('nested', OrderedDict([
                ('one', 1),
                ('two', 2),
                ('three', 3),
                ('four', 4)
        ]))
])
print(original)

content = yaml.dump(original, Dumper=OrderedDumper)
print(content)

data = yaml.load(content, Loader=OrderedLoader)
print(data)

assert original == data

content = yaml.dump(data, Dumper=OrderedDumper)
print(content)

                                   

output

OrderedDict([('one', 1), ('two', 2), ('three', 3), ('four', 4), ('nested', OrderedDict([('one', 1), ('two', 2), ('three', 3), ('four', 4)]))])
one: 1
two: 2
three: 3
four: 4
nested:
  one: 1
  two: 2
  three: 3
  four: 4

OrderedDict([('one', 1), ('two', 2), ('three', 3), ('four', 4), ('nested', OrderedDict([('one', 1), ('two', 2), ('three', 3), ('four', 4)]))])
one: 1
two: 2
three: 3
four: 4
nested:
  one: 1
  two: 2
  three: 3
  four: 4

requirement.txt

PyYAML==5.3