staff.py

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# example of macro to read data from an ascii file and
# create a root file with a Tree.
#
# NOTE: comparing the results of this macro with those of staff.C, you'll
# notice that the resultant file is a couple of bytes smaller, because the
# code below strips all white-spaces, whereas the .C version does not.

import re, array, os
from ROOT import *


### a C/C++ structure is required, to allow memory based access
gROOT.ProcessLine(
"struct staff_t {\
   Int_t           Category;\
   UInt_t          Flag;\
   Int_t           Age;\
   Int_t           Service;\
   Int_t           Children;\
   Int_t           Grade;\
   Int_t           Step;\
   Int_t           Hrweek;\
   Int_t           Cost;\
   Char_t          Division[4];\
   Char_t          Nation[3];\
};" );

### function to read in data from ASCII file and fill the ROOT tree
def fillTree():

   staff = staff_t()

 # The input file cern.dat is a copy of the CERN staff data base
 # from 1988

   f = TFile( 'staff.root', 'RECREATE' )
   tree = TTree( 'T', 'staff data from ascii file' )
   tree.Branch( 'staff', staff, 'Category/I:Flag:Age:Service:Children:Grade:Step:Hrweek:Cost' )
   tree.Branch( 'Divisions', AddressOf( staff, 'Division' ), 'Division/C' )
   tree.Branch( 'Nation', AddressOf( staff, 'Nation' ), 'Nation/C' )

 # note that the branches Division and Nation cannot be on the first branch
   fname = os.path.join(os.path.dirname(__file__),'../tree/cernstaff.dat')
   for line in open(fname).readlines():
      t = filter( lambda x: x, re.split( '\s+', line ) )
      staff.Category = int(t[0])             # assign as integers
      staff.Flag     = int(t[1])
      staff.Age      = int(t[2])
      staff.Service  = int(t[3])
      staff.Children = int(t[4])
      staff.Grade    = int(t[5])
      staff.Step     = int(t[6])
      staff.Hrweek   = int(t[7])
      staff.Cost     = int(t[8])
      staff.Division = t[9]                  # assign as strings
      staff.Nation   = t[10]

      tree.Fill()

   tree.Print()
   tree.Write()

#### run fill function if invoked on CLI
if __name__ == '__main__':
   fillTree()