Created
February 25, 2011 19:54
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Load YAML mappings as ordered dictionaries
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| import yaml | |
| import yaml.constructor | |
| try: | |
| # included in standard lib from Python 2.7 | |
| from collections import OrderedDict | |
| except ImportError: | |
| # try importing the backported drop-in replacement | |
| # it's available on PyPI | |
| from ordereddict import OrderedDict | |
| class OrderedDictYAMLLoader(yaml.Loader): | |
| """ | |
| A YAML loader that loads mappings into ordered dictionaries. | |
| """ | |
| def __init__(self, *args, **kwargs): | |
| yaml.Loader.__init__(self, *args, **kwargs) | |
| self.add_constructor(u'tag:yaml.org,2002:map', type(self).construct_yaml_map) | |
| self.add_constructor(u'tag:yaml.org,2002:omap', type(self).construct_yaml_map) | |
| def construct_yaml_map(self, node): | |
| data = OrderedDict() | |
| yield data | |
| value = self.construct_mapping(node) | |
| data.update(value) | |
| def construct_mapping(self, node, deep=False): | |
| if isinstance(node, yaml.MappingNode): | |
| self.flatten_mapping(node) | |
| else: | |
| raise yaml.constructor.ConstructorError(None, None, | |
| 'expected a mapping node, but found %s' % node.id, node.start_mark) | |
| mapping = OrderedDict() | |
| for key_node, value_node in node.value: | |
| key = self.construct_object(key_node, deep=deep) | |
| try: | |
| hash(key) | |
| except TypeError, exc: | |
| raise yaml.constructor.ConstructorError('while constructing a mapping', | |
| node.start_mark, 'found unacceptable key (%s)' % exc, key_node.start_mark) | |
| value = self.construct_object(value_node, deep=deep) | |
| mapping[key] = value | |
| return mapping | |
| if __name__ == '__main__': | |
| import textwrap | |
| sample = """ | |
| one: | |
| two: fish | |
| red: fish | |
| blue: fish | |
| two: | |
| a: yes | |
| b: no | |
| c: null | |
| """ | |
| data = yaml.load(textwrap.dedent(sample), OrderedDictYAMLLoader) | |
| assert type(data) is OrderedDict | |
| print data |
Is there a license for this code snippet? Can I use it?
Licensing this with anything would sure help out the commercial Internet community.
MIT license on oyaml here https://github.com/wimglenn/oyaml
From PyYAML 5.1 on, a dictionary can be dumped without reordering keys with:
yaml.dump(data, sort_keys=False)Saw this on stack overflow and it works, the docs don't seem to be updated though...
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Hi,
I have a big code base and so far I used vanilla yaml load like this yaml.load(s, Loader=yaml.BaseLoader)
I tried your OrderedDictYAMLLoader but I pretty much get nothing from load now.
what is the exact diffrences, have you tested this in a real application maybe with nested dictionaries of diffrent length?
thanks