# Original author: D. Eppstein, UC Irvine, August 12, 2003.
# The original code at https://www.ics.uci.edu/~eppstein/PADS/ is public domain.
"""Functions for reading and writing graphs in the *sparse6* format.
The *sparse6* file format is a space-efficient format for large sparse
graphs. For small graphs or large dense graphs, use the *graph6* file
format.
For more information, see the `sparse6`_ homepage.
.. _sparse6: https://users.cecs.anu.edu.au/~bdm/data/formats.html
"""
import networkx as nx
from networkx.exception import NetworkXError
from networkx.readwrite.graph6 import data_to_n, n_to_data
from networkx.utils import not_implemented_for, open_file
__all__ = ["from_sparse6_bytes", "read_sparse6", "to_sparse6_bytes", "write_sparse6"]
def _generate_sparse6_bytes(G, nodes, header):
"""Yield bytes in the sparse6 encoding of a graph.
`G` is an undirected simple graph. `nodes` is the list of nodes for
which the node-induced subgraph will be encoded; if `nodes` is the
list of all nodes in the graph, the entire graph will be
encoded. `header` is a Boolean that specifies whether to generate
the header ``b'>>sparse6<<'`` before the remaining data.
This function generates `bytes` objects in the following order:
1. the header (if requested),
2. the encoding of the number of nodes,
3. each character, one-at-a-time, in the encoding of the requested
node-induced subgraph,
4. a newline character.
This function raises :exc:`ValueError` if the graph is too large for
the graph6 format (that is, greater than ``2 ** 36`` nodes).
"""
n = len(G)
if n >= 2**36:
raise ValueError(
"sparse6 is only defined if number of nodes is less than 2 ** 36"
)
if header:
yield b">>sparse6<<"
yield b":"
for d in n_to_data(n):
yield str.encode(chr(d + 63))
k = 1
while 1 << k < n:
k += 1
def enc(x):
"""Big endian k-bit encoding of x"""
return [1 if (x & 1 << (k - 1 - i)) else 0 for i in range(k)]
edges = sorted((max(u, v), min(u, v)) for u, v in G.edges())
bits = []
curv = 0
for v, u in edges:
if v == curv: # current vertex edge
bits.append(0)
bits.extend(enc(u))
elif v == curv + 1: # next vertex edge
curv += 1
bits.append(1)
bits.extend(enc(u))
else: # skip to vertex v and then add edge to u
curv = v
bits.append(1)
bits.extend(enc(v))
bits.append(0)
bits.extend(enc(u))
if k < 6 and n == (1 << k) and ((-len(bits)) % 6) >= k and curv < (n - 1):
# Padding special case: small k, n=2^k,
# more than k bits of padding needed,
# current vertex is not (n-1) --
# appending 1111... would add a loop on (n-1)
bits.append(0)
bits.extend([1] * ((-len(bits)) % 6))
else:
bits.extend([1] * ((-len(bits)) % 6))
data = [
(bits[i + 0] << 5)
+ (bits[i + 1] << 4)
+ (bits[i + 2] << 3)
+ (bits[i + 3] << 2)
+ (bits[i + 4] << 1)
+ (bits[i + 5] << 0)
for i in range(0, len(bits), 6)
]
for d in data:
yield str.encode(chr(d + 63))
yield b"\n"
[docs]
@nx._dispatchable(graphs=None, returns_graph=True)
def from_sparse6_bytes(string):
"""Read an undirected graph in sparse6 format from string.
Parameters
----------
string : string
Data in sparse6 format
Returns
-------
G : Graph
Raises
------
NetworkXError
If the string is unable to be parsed in sparse6 format
Examples
--------
>>> G = nx.from_sparse6_bytes(b":A_")
>>> sorted(G.edges())
[(0, 1), (0, 1), (0, 1)]
See Also
--------
read_sparse6, write_sparse6
References
----------
.. [1] Sparse6 specification
<https://users.cecs.anu.edu.au/~bdm/data/formats.html>
"""
if string.startswith(b">>sparse6<<"):
string = string[11:]
if not string.startswith(b":"):
raise NetworkXError("Expected leading colon in sparse6")
chars = [c - 63 for c in string[1:]]
n, data = data_to_n(chars)
k = 1
while 1 << k < n:
k += 1
def parseData():
"""Returns stream of pairs b[i], x[i] for sparse6 format."""
chunks = iter(data)
d = None # partial data word
dLen = 0 # how many unparsed bits are left in d
while 1:
if dLen < 1:
try:
d = next(chunks)
except StopIteration:
return
dLen = 6
dLen -= 1
b = (d >> dLen) & 1 # grab top remaining bit
x = d & ((1 << dLen) - 1) # partially built up value of x
xLen = dLen # how many bits included so far in x
while xLen < k: # now grab full chunks until we have enough
try:
d = next(chunks)
except StopIteration:
return
dLen = 6
x = (x << 6) + d
xLen += 6
x = x >> (xLen - k) # shift back the extra bits
dLen = xLen - k
yield b, x
v = 0
G = nx.MultiGraph()
G.add_nodes_from(range(n))
multigraph = False
for b, x in parseData():
if b == 1:
v += 1
# padding with ones can cause overlarge number here
if x >= n or v >= n:
break
elif x > v:
v = x
else:
if G.has_edge(x, v):
multigraph = True
G.add_edge(x, v)
if not multigraph:
G = nx.Graph(G)
return G
[docs]
def to_sparse6_bytes(G, nodes=None, header=True):
"""Convert an undirected graph to bytes in sparse6 format.
Parameters
----------
G : Graph (undirected)
nodes: list or iterable
Nodes are labeled 0...n-1 in the order provided. If None the ordering
given by ``G.nodes()`` is used.
header: bool
If True add '>>sparse6<<' bytes to head of data.
Raises
------
NetworkXNotImplemented
If the graph is directed.
ValueError
If the graph has at least ``2 ** 36`` nodes; the sparse6 format
is only defined for graphs of order less than ``2 ** 36``.
Examples
--------
>>> nx.to_sparse6_bytes(nx.path_graph(2))
b'>>sparse6<<:An\\n'
See Also
--------
to_sparse6_bytes, read_sparse6, write_sparse6_bytes
Notes
-----
The returned bytes end with a newline character.
The format does not support edge or node labels.
References
----------
.. [1] Graph6 specification
<https://users.cecs.anu.edu.au/~bdm/data/formats.html>
"""
if nodes is not None:
G = G.subgraph(nodes)
G = nx.convert_node_labels_to_integers(G, ordering="sorted")
return b"".join(_generate_sparse6_bytes(G, nodes, header))
[docs]
@open_file(0, mode="rb")
@nx._dispatchable(graphs=None, returns_graph=True)
def read_sparse6(path):
"""Read an undirected graph in sparse6 format from path.
Parameters
----------
path : file or string
File or filename to write.
Returns
-------
G : Graph/Multigraph or list of Graphs/MultiGraphs
If the file contains multiple lines then a list of graphs is returned
Raises
------
NetworkXError
If the string is unable to be parsed in sparse6 format
Examples
--------
You can read a sparse6 file by giving the path to the file::
>>> import tempfile
>>> with tempfile.NamedTemporaryFile(delete=False) as f:
... _ = f.write(b">>sparse6<<:An\\n")
... _ = f.seek(0)
... G = nx.read_sparse6(f.name)
>>> list(G.edges())
[(0, 1)]
You can also read a sparse6 file by giving an open file-like object::
>>> import tempfile
>>> with tempfile.NamedTemporaryFile() as f:
... _ = f.write(b">>sparse6<<:An\\n")
... _ = f.seek(0)
... G = nx.read_sparse6(f)
>>> list(G.edges())
[(0, 1)]
See Also
--------
read_sparse6, from_sparse6_bytes
References
----------
.. [1] Sparse6 specification
<https://users.cecs.anu.edu.au/~bdm/data/formats.html>
"""
glist = []
for line in path:
line = line.strip()
if not len(line):
continue
glist.append(from_sparse6_bytes(line))
if len(glist) == 1:
return glist[0]
else:
return glist
[docs]
@not_implemented_for("directed")
@open_file(1, mode="wb")
def write_sparse6(G, path, nodes=None, header=True):
"""Write graph G to given path in sparse6 format.
Parameters
----------
G : Graph (undirected)
path : file or string
File or filename to write
nodes: list or iterable
Nodes are labeled 0...n-1 in the order provided. If None the ordering
given by G.nodes() is used.
header: bool
If True add '>>sparse6<<' string to head of data
Raises
------
NetworkXError
If the graph is directed
Examples
--------
You can write a sparse6 file by giving the path to the file::
>>> import tempfile
>>> with tempfile.NamedTemporaryFile(delete=False) as f:
... nx.write_sparse6(nx.path_graph(2), f.name)
... print(f.read())
b'>>sparse6<<:An\\n'
You can also write a sparse6 file by giving an open file-like object::
>>> with tempfile.NamedTemporaryFile() as f:
... nx.write_sparse6(nx.path_graph(2), f)
... _ = f.seek(0)
... print(f.read())
b'>>sparse6<<:An\\n'
See Also
--------
read_sparse6, from_sparse6_bytes
Notes
-----
The format does not support edge or node labels.
References
----------
.. [1] Sparse6 specification
<https://users.cecs.anu.edu.au/~bdm/data/formats.html>
"""
if nodes is not None:
G = G.subgraph(nodes)
G = nx.convert_node_labels_to_integers(G, ordering="sorted")
for b in _generate_sparse6_bytes(G, nodes, header):
path.write(b)
