Re: [Q] How to compose, serialize, and emit in PyYAML?

Makoto Kuwata wrote:
> Hi,
> I'm investigating PyYAML 3.05 and have some questions.
> 
> Q1. How to compose nodes from event list?
> Q2. How to serialize node into event list?
> Q3. How to emit event list into stram?

PyYAML has no direct support for Q1 and Q2. For Q3, you may use:

yaml.emit(events)

Basically, PyYAML only supports serializing events/nodes/objects to the 
output YAML stream and deserializing tokens/events/nodes/objects from 
the input YAML stream.  However it is relatively easy to write 
nodes->events and events->nodes converters using existing PyYAML 
infrastructure.

For Q1 (events to nodes):

class EventsToNodes(yaml.composer.Composer, yaml.resolver.Resolver):

     def __init__(self, events):
         super(EventsToNodes, self).__init__()
         if isinstance(events, list):
             events = iter(events)
         self.events = events
         self.current_event = None

     def check_event(self, *choices):
         if self.current_event is None:
             self.current_event = self.events.next()
         if not choices:
             return True
         for choice in choices:
             if isinstance(self.current_event, choice):
                 return True
         return False

     def peek_event(self):
         if self.current_event is None:
             self.current_event = self.events.next()
         return self.current_event

     def get_event(self):
         if self.current_event is None:
             self.current_event = self.events.next()
         value = self.current_event
         self.current_event = None
         return value

node = yaml.compose(events, Loader=EventsToNodes)
print node

For Q2 (nodes to events):

class NodesToEvents(yaml.serializer.Serializer, yaml.resolver.Resolver):

     def __init__(self, events, **parameters):
         super(NodesToEvents, self).__init__()
         self.events = events

     def emit(self, event):
         self.events.append(event)

events = []
yaml.serialize(node, events, Dumper=NodesToEvents)
print events


Thanks,
Kirill

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