NetworkX

```"""
**************
SparseGraph 6
**************
Read graphs in graph6 and sparse6 format.

Format
------

"graph6 and sparse6 are formats for storing undirected graphs in a
compact manner, using only printable ASCII characters. Files in these
formats have text type and contain one line per graph."
http://cs.anu.edu.au/~bdm/data/formats.html

See http://cs.anu.edu.au/~bdm/data/formats.txt for details.
"""
# 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)"""
#    Aric Hagberg <hagberg@lanl.gov>
#    Dan Schult <dschult@colgate.edu>
#    Pieter Swart <swart@lanl.gov>

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

# graph6

"""Read simple undirected graphs in graph6 format from path.

Returns a single Graph.
"""

[docs]def parse_graph6(str):
"""Read a simple undirected graph in graph6 format from string.

Returns a single Graph.
"""
def bits():
"""Return sequence of individual bits from 6-bit-per-value
list of data values."""
for d in data:
for i in [5,4,3,2,1,0]:
yield (d>>i)&1

if str.startswith('>>graph6<<'):
str = str[10:]
data = graph6data(str)
n, data = graph6n(data)
nd = (n*(n-1)//2 + 5) // 6
if len(data) != nd:
raise NetworkXError(\
'Expected %d bits but got %d in graph6' % (n*(n-1)//2, len(data)*6))

G=nx.Graph()
for (i,j),b in zip([(i,j) for j in range(1,n) for i in range(j)], bits()):
return G

@open_file(0,mode='rt')
"""Read simple undirected graphs in graph6 format from path.

Returns a list of Graphs, one for each line in file.
"""
glist=[]
for line in path:
line = line.strip()
if not len(line): continue
glist.append(parse_graph6(line))
return glist

# sparse6

"""Read simple undirected graphs in sparse6 format from path.

Returns a single MultiGraph."""

@open_file(0,mode='rt')
"""Read undirected graphs in sparse6 format from path.

Returns a list of MultiGraphs, one for each line in file."""
glist=[]
for line in path:
line = line.strip()
if not len(line): continue
glist.append(parse_sparse6(line))
return glist

[docs]def parse_sparse6(string):
"""Read undirected graph in sparse6 format from string.

Returns a MultiGraph.
"""
if string.startswith('>>sparse6<<'):
string = str[10:]
if not string.startswith(':'):
raise NetworkXError('Expected colon in sparse6')
n, data = graph6n(graph6data(string[1:]))
k = 1
while 1<<k < n:
k += 1

def parseData():
"""Return 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:
d = next(chunks)
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
d = next(chunks)
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()

for b,x in parseData():
if b: v += 1
if x >= n: break # padding with ones can cause overlarge number here
elif x > v: v = x
else:

return G

# helper functions

def graph6data(str):
"""Convert graph6 character sequence to 6-bit integers."""
v = [ord(c)-63 for c in str]
if min(v) < 0 or max(v) > 63:
return None
return v

def graph6n(data):
"""Read initial one or four-unit value from graph6 sequence.
Return value, rest of seq."""
if data[0] <= 62:
return data[0], data[1:]
return (data[1]<<12) + (data[2]<<6) + data[3], data[4:]
```