staff.py File Reference

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 os
 
import ROOT
from ROOT import TFile, TTree, addressof, gROOT
 
## 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 staff():
 
    staff = ROOT.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(str(ROOT.gROOT.GetTutorialDir()), "io", "tree", "cernstaff.dat")
    with open(fname) as file:
        for line in file.readlines():
            t = line.split()
            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()
 
    f.Close()
 
 
#### run fill function if invoked on CLI
if __name__ == "__main__":
    staff()

Author

Wim Lavrijsen

Definition in file staff.py.