old_contents: #!/usr/bin/env python
  # Tai Sakuma <sakuma@cern.ch>
  import pandas as pd
  
  ##__________________________________________________________________||
  d1 = pd.read_table('tbl_process.txt', delim_whitespace = True)
  d2 = pd.read_table('tbl_component_met.txt', delim_whitespace = True)
  d3 = pd.read_table('tbl_nevt.txt', delim_whitespace = True)
  d4 = pd.read_table('tbl_xsec.txt', delim_whitespace = True)
  
  d = pd.merge(d1, d2)
  d = d.groupby(['phasespace', 'process', 'met']).sum().reset_index()
  e = pd.merge(d1, d3)
  e = e.groupby(['phasespace', 'process']).sum().reset_index()
  e = pd. merge(e, d4)
  d = pd.merge(d, e)
  lumi = 4000
  d.n = d.n*d.xsec/d.nevt*lumi
  d.nvar = d.nvar*(d.xsec/d.nevt*lumi)**2
  d = d.drop('nevt', 1)
  d = d.drop('xsec', 1)
  d = d.groupby(['process', 'met']).sum().reset_index()
  
  f = open('tbl_out_python.txt', 'w')
  d.to_string(f, index = False)
  f.write("\n")
  f.close()
  
  ##__________________________________________________________________||
  
new_contents: #!/usr/bin/env python
  # Tai Sakuma <sakuma@cern.ch>
  import pandas as pd
  
  ##__________________________________________________________________||
  d1 = pd.read_table('tbl_process.txt', delim_whitespace = True)
  d2 = pd.read_table('tbl_component_met.txt', delim_whitespace = True)
  d3 = pd.read_table('tbl_nevt.txt', delim_whitespace = True)
  d4 = pd.read_table('tbl_xsec.txt', delim_whitespace = True)
  
  d = pd.merge(d1, d2)
  d = d.groupby(['phasespace', 'process', 'met']).sum().reset_index()
  e = pd.merge(d1, d3)
  e = e.groupby(['phasespace', 'process']).sum().reset_index()
  e = pd. merge(e, d4)
  d = pd.merge(d, e)
  lumi = 4000
  d.n = d.n*d.xsec/d.nevt*lumi
  d.nvar = d.nvar*(d.xsec/d.nevt*lumi)**2
  del d['nevt']
  del d['xsec']
  d = d.groupby(['process', 'met']).sum().reset_index()
  
  f = open('tbl_out_python.txt', 'w')
  d.to_string(f, index = False)
  f.write("\n")
  f.close()
  
  ##__________________________________________________________________||
  
subject: use del instead of drop in yield.py