File: leda.py

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"""
Read graphs in LEDA format.

LEDA is a C++ class library for efficient data types and algorithms.

Format
------
See http://www.algorithmic-solutions.info/leda_guide/graphs/leda_native_graph_fileformat.html

"""
# Original author: D. Eppstein, UC Irvine, August 12, 2003.
# The original code at http://www.ics.uci.edu/~eppstein/PADS/ is public domain.
__author__ = """Aric Hagberg (hagberg@lanl.gov)"""
#    Copyright (C) 2004-2010 by 
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>
#    All rights reserved.
#    BSD license.

__all__ = ['read_leda', 'parse_leda']

import networkx as nx 
from networkx.exception import NetworkXError
from networkx.utils import open_file, is_string_like

@open_file(0,mode='rb')
def read_leda(path, encoding='UTF-8'):
    """Read graph in LEDA format from path.

    Parameters
    ----------
    path : file or string
       File or filename to read.  Filenames ending in .gz or .bz2  will be 
       uncompressed.

    Returns
    -------
    G : NetworkX graph

    Examples
    --------
    G=nx.read_leda('file.leda')
 
    References
    ----------
    .. [1] http://www.algorithmic-solutions.info/leda_guide/graphs/leda_native_graph_fileformat.html
    """
    lines=(line.decode(encoding) for line in path)
    G=parse_leda(lines)
    return G


def parse_leda(lines):
    """Read graph in LEDA format from string or iterable.

    Parameters
    ----------
    lines : string or iterable
       Data in LEDA format.

    Returns
    -------
    G : NetworkX graph

    Examples
    --------
    G=nx.parse_leda(string)
 
    References
    ----------
    .. [1] http://www.algorithmic-solutions.info/leda_guide/graphs/leda_native_graph_fileformat.html
    """
    if is_string_like(lines): lines=iter(lines.split('\n'))
    lines = iter([line.rstrip('\n') for line in lines \
            if not (line.startswith('#') or line.startswith('\n') or line=='')])
    for i in range(3):
        next(lines)
    # Graph
    du = int(next(lines)) # -1=directed, -2=undirected
    if du==-1:
        G = nx.DiGraph()
    else:
        G = nx.Graph()
        
    # Nodes
    n =int(next(lines)) # number of nodes
    node={}
    for i in range(1,n+1):  # LEDA counts from 1 to n
        symbol=next(lines).rstrip().strip('|{}|  ')
        if symbol=="": symbol=str(i) # use int if no label - could be trouble
        node[i]=symbol

    G.add_nodes_from([s for i,s in node.items()])
	
    # Edges
    m = int(next(lines)) # number of edges
    for i in range(m):
        try:
            s,t,reversal,label=next(lines).split()
        except:
            raise NetworkXError('Too few fields in LEDA.GRAPH edge %d'%(i+1))
        # BEWARE: no handling of reversal edges
        G.add_edge(node[int(s)],node[int(t)],label=label[2:-2])
    return G