"""Unary operations on graphs"""
#    Copyright (C) 2004-2012 by
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>
#    All rights reserved.
#    BSD license.
import networkx as nx
from networkx.utils import is_string_like
__author__ = """\n""".join(['Aric Hagberg (hagberg@lanl.gov)',
                           'Pieter Swart (swart@lanl.gov)',
                           'Dan Schult(dschult@colgate.edu)'])
__all__ = ['complement']

def complement(G, name=None):
    """Return the graph complement of G.

    Parameters
    ----------
    G : graph
       A NetworkX graph

    name : string
       Specify name for new graph

    Returns
    -------
    GC : A new graph.

    Notes
    ------
    Note that complement() does not create self-loops and also
    does not produce parallel edges for MultiGraphs.

    Graph, node, and edge data are not propagated to the new graph.
    """
    if name is None:
        name="complement(%s)"%(G.name)
    R=G.__class__()
    R.name=name
    R.add_nodes_from(G)
    R.add_edges_from( ((n,n2)
                       for n,nbrs in G.adjacency_iter()
                       for n2 in G if n2 not in nbrs
                       if n != n2) )
    return R