I'm trying to draw any graph in NetworkX, but get nothing, not even errors:

import networkx as nx
import matplotlib.pyplot as plt
g1=nx.petersen_graph()
nx.draw(g1)

Add to the end:

plt.show()

import networkx as nx
import matplotlib.pyplot as plt
g1 = nx.petersen_graph()
nx.draw(g1)
plt.show()

When run from an interactive shell where plt.ion() has been called, the plt.show() is not needed. This is probably why it is omitted in a lot of examples.

If you run these commands from a script (where plt.ion() has not been called), the plt.show() is needed. plt.ion() is okay for interactive sessions, but is not recommended for scripts.