align map-values at dump

[az@…]

here something that aligns values of maps in vertical column (depending on longest key, or u can change the logic). it's somewhat patchwork, but works.

#yaml_align.py
import yaml
from yaml.nodes import ScalarNode

class Dumper_MapAlignValues( object):
    'inherit + Dumper'

    #Representer.represent_mapping
    def represent_mapping(self, tag, mapping, flow_style=None):
        node = yaml.Dumper.represent_mapping( self, tag, mapping, flow_style)
        node._keywidth = 0
        if mapping:
            keys = [ k for k,v in node.value]
            simplekeys = sum( isinstance( k,ScalarNode) for k in keys) == len( node.value)
            if simplekeys:
                node._keywidth = max( len( str(k.value)) for k in keys)
        return node

    #Serializer.serialize_node
    def serialize_node(self, node, parent, index):
        if (node not in self.serialized_nodes
            and isinstance( node, ScalarNode)
            and getattr( parent, '_keywidth', None)  #mapping with _keywidth
            and index is not None   #this=value, index=key in (key,value)
            ):
                node.style = ( parent._keywidth - len( index.value ), node.style)
        return yaml.Dumper.serialize_node( self, node, parent, index)

    #Emitter.choose_scalar_style
    def choose_scalar_style(self):
        alignindent = None
        if isinstance( self.event.style, tuple):
            alignindent, self.event.style = self.event.style
        r = yaml.Dumper.choose_scalar_style( self)
        if alignindent is not None and r in ['', "'", '"']:
            data = ' '*alignindent
            self.column += len(data)
            if self.encoding:
                data = data.encode(self.encoding)
            self.stream.write(data)
        return r

'''usage:
class Dumper( yaml_align.Dumper_MapAlignValues, yaml.Dumper):
     pass

tt = '''
one: 1
two: 2
three: 3
four: 4
eleven: 11
'''
dd = yaml.load( tt)

print yaml.dump( dd, default_flow_style= False, Dumper= Dumper)

eleven: 11
four:   4
one:    1
three:  3
two:    2