<｜begin▁of▁sentence｜>### Instruction:
Given a path graph with 4 nodes created in NetworkX, how can the 'freeze' API function be used to prevent the graph from being modified by the addition or removal of nodes or edges, and what is the expected behavior when attempting to modify the frozen graph?
### Response:
import networkx as nx

# Create a path graph with 4 nodes
G = nx.path_graph(4)

# Freeze the graph to prevent further changes
gf = nx.freeze(G)

# Attempt to add an edge to the frozen graph
try:
    gf.add_edge(4, 5)
except nx.NetworkXError as err:
    print(str(err))  # This will print an error message
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