def to_string(self):
        '''
        API: to_string(self)
        Description:
        Returns string representation of node in dot language.
        Return:
            String representation of node.
        '''
        node = list()
        node.append(quote_if_necessary(str(self.name)))
        node.append(' [')
        flag = False
        for a in self.attr:
            flag = True
            node.append(a)
            node.append('=')
            node.append(quote_if_necessary(str(self.attr[a])))
            node.append(', ')
        if flag is True:
            node = node[:-1]
        node.append(']')
        return ''.join(node)