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Load YAML mappings as ordered dictionaries

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yaml_ordered_dict.py
Python
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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

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

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