Reaction KO FBA and pFBA

import cobra.test
from cobra.flux_analysis import pfba
stm = cobra.test.create_test_model("salmonella")
stm_fba = stm.optimize()
stm_pfba = pfba(stm)
pfk_stm = stm.reactions.get_by_id("PFK")

with stm:
    print ("STM PFK before KO: ", pfk_stm.lower_bound, "< pfk <", pfk_stm.upper_bound)
    print ("""# Absolute predicted flux before PFK KO
1. By FBA   : """, stm_fba.fluxes.abs().sum())
    print ("2. By pFBA  : ", stm_pfba.objective_value)
    print ("Diff. betn FBA and pFBA : ", stm_fba.fluxes.abs().sum() - 
          stm_pfba.objective_value)

    stm.reactions.PFK.knock_out()

    stm_fba = stm.optimize()
    stm_pfba = pfba(stm)
    
    print ("\nSTM PFK after KO: ", pfk_stm.lower_bound, "< pfk <", pfk_stm.upper_bound)
    print ("""# Absolute predicted flux after PFK KO
1. By FBA   : """, stm_fba.fluxes.abs().sum())
    print ("2. By pFBA  : ", stm_pfba.objective_value)
    print ("Diff. betn FBA and pFBA : ", stm_fba.fluxes.abs().sum() - 
          stm_pfba.objective_value)