Formatting the output of a custom class in PyYAML
I'm working on a simple example here, but the docs still confuse me a little.
Here's some sample code:
class A(yaml.YAMLObject):
yaml_tag = u'!A'
def __init__(self, val):
self.val = val
if __name__ == '__main__':
t = datetime.time()
a = A(t)
print yaml.dump(a)
print yaml.load(yaml.dump(a)).val == t
Output signal
! A val: !! python / object / apply: datetime.time ["\ 0 \ 0 \ 0 \ 0 \ 0 \ 0"]
True
So it appears to be faithfully d- / serialized, but the default time format leaves a lot to be desired. How can I make it prettier while keeping the power of powerful dumps / loads?
thank
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Override time format for all times in a document
You can define your own serialization format for any instances datetime.time
in your documents using PyYAML's "representers" and "constructors" .
import datetime
import yaml
time_format = '%H:%M:%S'
def time_representer(dumper, data):
return dumper.represent_scalar(u'!time', data.strftime(time_format))
def time_constructor(loader, node):
value = loader.construct_scalar(node)
return datetime.datetime.strptime(value, time_format).time()
yaml.add_representer(datetime.time, time_representer)
yaml.add_constructor(u'!time', time_constructor)
class A(yaml.YAMLObject):
yaml_tag = u'!A'
def __init__(self, val):
self.val = val
if __name__ == '__main__':
t = datetime.time()
a = A(t)
print yaml.dump(a, default_flow_style=False)
print yaml.load(yaml.dump(a)).val == t
The output will be:
!A
val: !time '00:00:00'
True
Override time format for specific class only
You can also define how to a specific class is serialized and deserialized. So you can just change the presentation time for only A
. Docs for YAMLObject
import datetime
import yaml
time_format = '%H:%M:%S'
class A(yaml.YAMLObject):
yaml_tag = u'!A'
def __init__(self, val):
self.val = val
@classmethod
def to_yaml(cls, dumper, data):
dict_representation = {
'val':data.val.strftime(time_format)
}
node = dumper.represent_mapping(u'!A', dict_representation)
return node
@classmethod
def from_yaml(cls, loader, node):
dict_representation = loader.construct_mapping(node)
val = datetime.datetime.strptime(
dict_representation['val'], time_format).time()
return A(val)
if __name__ == '__main__':
t = datetime.time()
a = A(t)
print yaml.dump([t,a], default_flow_style=False)
loaded = yaml.load(yaml.dump([t,a]))
print loaded[0] == t
print loaded[1].val == t
The output will be:
- !!python/object/apply:datetime.time
- "\0\0\0\0\0\0"
- !A
val: 00:00:00
True
True
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