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import yaml
import yaml.constructor
###############################################################
# Procedures to preserve order of config file for readability #
###############################################################
# http://stackoverflow.com/questions/5121931/in-python-how-can-you-load-yaml-mappings-as-ordereddicts
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
# https://gist.github.com/miracle2k/3184458
"""Make PyYAML output an OrderedDict.
It will do so fine if you use yaml.dump(), but that generates ugly,
non-standard YAML code.
To use yaml.safe_dump(), you need the following.
"""
def represent_odict(dump, tag, mapping, flow_style=None):
"""Like BaseRepresenter.represent_mapping, but does not issue the sort().
"""
value = []
node = yaml.MappingNode(tag, value, flow_style=flow_style)
if dump.alias_key is not None:
dump.represented_objects[dump.alias_key] = node
best_style = True
if hasattr(mapping, 'items'):
mapping = mapping.items()
for item_key, item_value in mapping:
node_key = dump.represent_data(item_key)
node_value = dump.represent_data(item_value)
if not (isinstance(node_key, yaml.ScalarNode) and not node_key.style):
best_style = False
if not (isinstance(node_value, yaml.ScalarNode) and not node_value.style):
best_style = False
value.append((node_key, node_value))
if flow_style is None:
if dump.default_flow_style is not None:
node.flow_style = dump.default_flow_style
else:
node.flow_style = best_style
return node
# Sample of how it would be dumped and not; will update later to be more of a python module. Just dumping to gist for now
if __name__ == "__main__":
# Write out ordered YAML
with open("/config.yaml", "w") as f:
yaml.SafeDumper.add_representer(OrderedDict,
lambda dumper, value: represent_odict(dumper, u'tag:yaml.org,2002:map', value))
f.write(yaml.safe_dump(config))
# Read in ordered YAML
with open("/config.yaml") as f:
config = yaml.load(f, OrderedDictYAMLLoader)
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