How to use the pydot.Common function in pydot

# No point in having nodes setting any defaults if the don't set
        # any attributes...
        #
        if node in ('graph', 'node', 'edge') and len(node_attr) == 0:
            return ''
            
        node_attr = ', '.join(node_attr)

        if node_attr:
            node += ' [' + node_attr + ']'

        return node + ';'



class Edge(object,  Common ):
    """A graph edge.
    
    This class represents a graph's edge with all its attributes.
    
    edge(src, dst, attribute=value, ...)
    
    src: source node's name
    dst: destination node's name
    
    All the attributes defined in the Graphviz dot language should
    be supported.
    
 	Attributes can be set through the dynamically generated methods:
    
     set_[attribute name], i.e. set_label, set_fontname

#
        if node in ('graph', 'node', 'edge') and len(node_attr) == 0:
            return ''
        
        ### Modified to auto-wrap of each attribute line. 2015-05 by Vincent.H
        node_attr = (', \n'+' '*(len(node)+2)).join(node_attr)
        ### ------------------------------------------------------------------
        
        if node_attr:
            node += ' [' + node_attr + ']'

        return node + ';'



class Edge(object,  Common ):
    """A graph edge.
    
    This class represents a graph's edge with all its attributes.
    
    edge(src, dst, attribute=value, ...)
    
    src: source node's name
    dst: destination node's name
    
    All the attributes defined in the Graphviz dot language should
    be supported.
    
 	Attributes can be set through the dynamically generated methods:
    
     set_[attribute name], i.e. set_label, set_fontname

indent_len += len(x)+1
        indent_len += 2

        edge_attr = (', \n'+' '*indent_len).join(edge_attr)
        ### ------------------------------------------------------------------
        
        if edge_attr:
            edge.append( ' [' + edge_attr + ']' )

        return ' '.join(edge) + ';'
    
    
    
    
    
class Graph(object, Common):
    """Class representing a graph in Graphviz's dot language.

    This class implements the methods to work on a representation
    of a graph in Graphviz's dot language.
    
    graph(  graph_name='G', graph_type='digraph',
        strict=False, suppress_disconnected=False, attribute=value, ...)
    
    graph_name:
        the graph's name
    graph_type:
        can be 'graph' or 'digraph'
    suppress_disconnected:
        defaults to False, which will remove from the
        graph any disconnected nodes.
    simplify:

self.value = value
    def __str__(self):
        return self.value


class InvocationException(Exception):
    """To indicate that a ploblem occurred while running any of the GraphViz executables.
    """
    def __init__(self, value):
        self.value = value
    def __str__(self):
        return self.value



class Node(object, Common):
    """A graph node.
    
    This class represents a graph's node with all its attributes.
    
    node(name, attribute=value, ...)
    
    name: node's name
    
    All the attributes defined in the Graphviz dot language should
    be supported.
    """

    def __init__(self, name = '', obj_dict = None, **attrs):
    
        #
        # Nodes will take attributes of all other types because the defaults

for e in g.get_node(name):
            return e
        for sg in g.get_subgraphs():
            e = self.get_node(name,sg)
            if e is not None:
                return e
        return None
    def subgraphs(self):
        return self.g.get_subgraphs()
    

    
    def __str__(self):
        return str(self.g)

pydot.Common.attr = property(lambda self: self.obj_dict['attributes'])
pydot.Subgraph.graph_attr = property(lambda self: self.obj_dict['attributes'])
pydot.Subgraph.name = property(lambda self: self.get_name())


if __name__ == "__main__":
    g = AGraph()
    g.add_node('1',label='foo')
    g.add_node('2',label='bar')
    g.add_edge('1','2','e1')
    g.add_subgraph(name='cluster_1',nbunch=['1','2'])
    g.add_node('3',label='foo')
    g.add_node('4',label='bar')
    g.add_edge('3','4','e1')
    g.add_subgraph(name='cluster_2',nbunch=['3','4'])
    print g
    g.layout()

edge_attr.append( '%s=%s' % (attr, quote_if_necessary(value) ) )
            else:
                edge_attr.append( attr )

        edge_attr = ', '.join(edge_attr)
        
        if edge_attr:
            edge.append( ' [' + edge_attr + ']' )

        return ' '.join(edge) + ';'
    
    
    
    
    
class Graph(object, Common):
    """Class representing a graph in Graphviz's dot language.

    This class implements the methods to work on a representation
    of a graph in Graphviz's dot language.
    
    graph(  graph_name='G', graph_type='digraph',
        strict=False, suppress_disconnected=False, attribute=value, ...)
    
    graph_name:
        the graph's name
    graph_type:
        can be 'graph' or 'digraph'
    suppress_disconnected:
        defaults to False, which will remove from the
        graph any disconnected nodes.
    simplify:

self.value = value
    def __str__(self):
        return self.value


class InvocationException(Exception):
    """Indicate ploblem while running any GraphViz executable.
    """
    def __init__(self, value):
        self.value = value
    def __str__(self):
        return self.value



class Node(Common):
    """A graph node.

    This class represents a graph's node with all its attributes.

    node(name, attribute=value, ...)

    name: node's name

    All the attributes defined in the Graphviz dot language should
    be supported.
    """

    def __init__(self, name = '', obj_dict = None, **attrs):

        #
        # Nodes will take attributes of

'%s=%s' % (attr, quote_if_necessary(value) ) )
            else:
                edge_attr.append( attr )

        edge_attr = ', '.join(edge_attr)

        if edge_attr:
            edge.append( ' [' + edge_attr + ']' )

        return ' '.join(edge) + ';'





class Graph(Common):
    """Class representing a graph in Graphviz's dot language.

    This class implements the methods to work on a representation
    of a graph in Graphviz's dot language.

    graph(  graph_name='G', graph_type='digraph',
        strict=False, suppress_disconnected=False, attribute=value, ...)

    graph_name:
        the graph's name
    graph_type:
        can be 'graph' or 'digraph'
    suppress_disconnected:
        defaults to False, which will remove from the
        graph any disconnected nodes.
    simplify:

self.value = value
    def __str__(self):
        return self.value


class InvocationException(Exception):
    """To indicate that a ploblem occurred while running any of the GraphViz executables.
    """
    def __init__(self, value):
        self.value = value
    def __str__(self):
        return self.value



class Node(object, Common):
    """A graph node.
    
    This class represents a graph's node with all its attributes.
    
    node(name, attribute=value, ...)
    
    name: node's name
    
    All the attributes defined in the Graphviz dot language should
    be supported.
    """

    def __repr__(self): return '' % self.obj_dict['name']

    def __init__(self, name = '', obj_dict = None, **attrs):

# No point in having nodes setting any defaults if the don't set
        # any attributes...
        #
        if node in ('graph', 'node', 'edge') and len(node_attr) == 0:
            return ''

        node_attr = ', '.join(node_attr)

        if node_attr:
            node += ' [' + node_attr + ']'

        return node + ';'



class Edge(Common):
    """A graph edge.

    This class represents a graph's edge with all its attributes.

    edge(src, dst, attribute=value, ...)

    src: source node
    dst: destination node

    `src` and `dst` can be specified as a `Node` object,
    or as the node's name string.

    All the attributes defined in the Graphviz dot language should
    be supported.

        Attributes can be set through the dynamically generated methods: