Read and write graphs.

Read and write graphs.

import io
import matplotlib.pyplot as plt
import networkx as nx

G = nx.grid_2d_graph(5, 5)  # 5x5 grid

# Use BytesIO as a virtual file handle.
# Replace with: `with open(<filename>, "wb") as fh:` to save to disk
fh = io.BytesIO()
# write edgelist to file
nx.write_edgelist(G, path=fh, delimiter=":")
# View file contents
print(fh.getvalue().decode())
# read edgelist from file
fh.seek(0)

(0, 0):(1, 0):{}
(0, 0):(0, 1):{}
(0, 1):(1, 1):{}
(0, 1):(0, 2):{}
(0, 2):(1, 2):{}
(0, 2):(0, 3):{}
(0, 3):(1, 3):{}
(0, 3):(0, 4):{}
(0, 4):(1, 4):{}
(1, 0):(2, 0):{}
(1, 0):(1, 1):{}
(1, 1):(2, 1):{}
(1, 1):(1, 2):{}
(1, 2):(2, 2):{}
(1, 2):(1, 3):{}
(1, 3):(2, 3):{}
(1, 3):(1, 4):{}
(1, 4):(2, 4):{}
(2, 0):(3, 0):{}
(2, 0):(2, 1):{}
(2, 1):(3, 1):{}
(2, 1):(2, 2):{}
(2, 2):(3, 2):{}
(2, 2):(2, 3):{}
(2, 3):(3, 3):{}
(2, 3):(2, 4):{}
(2, 4):(3, 4):{}
(3, 0):(4, 0):{}
(3, 0):(3, 1):{}
(3, 1):(4, 1):{}
(3, 1):(3, 2):{}
(3, 2):(4, 2):{}
(3, 2):(3, 3):{}
(3, 3):(4, 3):{}
(3, 3):(3, 4):{}
(3, 4):(4, 4):{}
(4, 0):(4, 1):{}
(4, 1):(4, 2):{}
(4, 2):(4, 3):{}
(4, 3):(4, 4):{}


0

Note that the original graph G had tuples as nodes. In order to recover the original node type, the data read from file must be properly interpreted using the nodetype kwarg

H = nx.read_edgelist(
    path=fh,
    # Convert from a string back to a tuple-of-int
    nodetype=lambda s: tuple(int(v) for v in s[1:-1].split(",")),
    delimiter=":",
)

nx.draw(H, pos={n: n for n in H})
plt.show()