<｜begin▁of▁sentence｜>### Instruction:
Given the Books about US politics graph which you can read from a GML file named polbooks.gml, can you utilize the EM algorithm from cdlib to perform community detection by specifying 3 as the desired number of communities? After performing the detection, can you then produce and print a JSON representation of the resulting NodeClustering object?
### Response:
import networkx as nx
from cdlib import algorithms

# Reading the graph from polbooks dataset
G = nx.read_gml('polbooks.gml')

# Running EM algorithm with a predefined number of communities (k=3)
communities = algorithms.em(G, k=3)

# Generating a JSON representation of the NodeClustering object
communities_json = communities.to_json()
print(communities_json)
<|EOT|>
