Using matplotlib subplots and gt.graph_draw's mplfig, graph is drawn modified before it is modified by code?

[52556427]

graph-tool 2.98, CachyOS Linux

Plotting a graph and the graph made maximally planar separately works as expected. But when I try to plot them besides each other on subplots, the original graph appears maximally planar before it is made so by gt.make_maximal_planar(g). Should this behaviour be expected? Is this a consequence of graph-tool calling C++ code?

import copy
import graph_tool.all as gt
from matplotlib import pyplot as plt

# Drawing graphs separately
g = gt.lattice([2, 2])
pos = gt.sfdp_layout(g)

gt.graph_draw(g, pos=pos)  # draws g with four edges as it should be

gt.make_maximal_planar(g)
pos = gt.sfdp_layout(g)
gt.graph_draw(g, pos=pos)  # draws g made maximally planar with now six edges as it should be

# Drawing graphs on subplots
g = gt.lattice([2, 2])
g_ = copy.deepcopy(g)
pos_ = gt.sfdp_layout(g_)
fig, axes = plt.subplots(nrows=1, ncols=3)

print(g.get_edges())
gt.graph_draw(g, pos=pos, mplfig=axes[0])  # draws g with six edges, before it is made maximally planar on line 30?

gt.make_maximal_planar(g)

print(g.get_edges())
gt.graph_draw(g, pos=pos, mplfig=axes[1])

print(g_.get_edges())
gt.graph_draw(g_, pos=pos_, mplfig=axes[2])

[tiago (Tiago Peixoto)]

When you call graph_draw() with the mplfig parameter, the drawing is not performed immediately, but only later when the figure is generated. What actually happens is that a graph artist gets included in the figure, but the drawing of that artist is only called at a later stage. If you modify the graph in the meantime, the drawing will reflect the modified graph, not the original one.