Capture pygraphviz image rendering without saving to a file?

Question

Does pygraphviz allow for you to render an image to a variable? I would like to serve up dynamic images via a webpage without having to render the graphs to disk.

Answer 1

According to the source code if you call the draw() method of an AGraph object while omitting the path argument (or setting it to None) it will return a bytes object instead of saving to a file. Do not forget to specify the format parameter.

For example, assuming that you already have an AGraph object named A, and you want to plot this graph, you could do this:

from IPython.display import Image, display

img_bytes = A.draw(format="png")
img = Image(img_bytes)
display(img)

Answer 2

I think is is what you want:

# https://stackoverflow.com/questions/28533111/plotting-networkx-graph-with-node-labels-defaulting-to-node-name

import dgl
import numpy as np
import torch

import networkx as nx

import matplotlib.pyplot as plt
import matplotlib.image as mpimg

from pathlib import Path

g = dgl.graph(([0, 0, 0, 0, 0], [1, 2, 3, 4, 5]), num_nodes=6)
print(f'{g=}')
print(f'{g.edges()=}')

# Since the actual graph is undirected, we convert it for visualization purpose.
g = g.to_networkx().to_undirected()
print(f'{g=}')

# relabel
int2label = {0: "app", 1: "cons", 2: "with", 3: "app3", 4: "app4", 5: "app5"}
g = nx.relabel_nodes(g, int2label)

# https://networkx.org/documentation/stable/reference/drawing.html#module-networkx.drawing.layout
g = nx.nx_agraph.to_agraph(g)
print(f'{g=}')
print(f'{g.string()=}')

# draw
g.layout()
g.draw("file.png")

# https://stackoverflow.com/questions/20597088/display-a-png-image-from-python-on-mint-15-linux
img = mpimg.imread('file.png')
plt.imshow(img)
plt.show()

# remove file https://stackoverflow.com/questions/6996603/how-to-delete-a-file-or-folder
Path('./file.png').expanduser().unlink()
# import os
# os.remove('./file.png')

you basically need to render the graph object explicitly from the file and then delete it (unfortunately idk of a better answer). For more details check out my long discussion on why I think pygraphviz is the way to go (and not networkx) for visualizing: https://stackoverflow.com/a/67439711/1601580

Answer 3

I couldn't find a way to do this without a file being involved, so I created this handy function:

import matplotlib.image as mpimg
import matplotlib.pyplot as plt
import networkx as nx
import pygraphviz

def plot_network(G: nx.DiGraph):
  ag = nx.nx_agraph.to_agraph(G)
  ag.layout(prog="dot")
  temp = tempfile.NamedTemporaryFile(delete=False)
  tempname = temp.name + ".png"
  ag.draw(tempname)
  img = mpimg.imread(tempname)
  plt.imshow(img)
  plt.show()
  os.remove(tempname)