input: Write a function to calculate the PageRank of nodes in a graph using NetworkX.
  assert page_rank(nx.DiGraph([(0, 1), (1, 2), (2, 0)])) == {0: 0.3333333333333333, 1: 0.3333333333333333, 2: 0.3333333333333333}
  assert page_rank(nx.DiGraph([(0, 1), (1, 2), (2, 0), (2, 3)])) == {0: 0.32142857142857145, 1: 0.32142857142857145, 2: 0.32142857142857145, 3: 0.03571428571428571}
  assert page_rank(nx.DiGraph([(0, 1), (1, 2), (2, 0), (3, 2)])) == {0: 0.3440860215053763, 1: 0.27297297297297297, 2: 0.3288288288288288, 3: 0.05411211211211211}
output: import networkx as nx
  
  def page_rank(graph):
      return nx.pagerank(graph)