text: import seaborn as sns
  sns.set()
  
  ### avoid coding problems ####
  import sys 
  reload(sys)
  sys.setdefaultencoding('gbk')
  ##############################
  
  from lifelines.datasets import load_waltons
  df = load_waltons()
  T = df['T']
  E = df['E']
  
  # fit
  from lifelines import NelsonAalenFitter
  naf = NelsonAalenFitter()
  
  # draw
  naf.fit(T, event_observed=E)
  naf.plot()
  import matplotlib.pyplot as plt
  plt.legend(frameon=True)
  plt.show()