PyROOT 使用

PyROOT

• pyROOT provides bindings for the classes in the root libraries
• it allows you to replace CINT with its interpreted c++ with (i)python

Installation

• compile ROOT with python support
• make sure that $ROOTSYS/lib is in your PYTHONPATH and LD_LIBRARY_PATH variables

Example 1 - TBrowser

In [2]: import ROOT

In [3]: tb = ROOT.TBrowser()

Example 2 - Opening TFiles

In [4]: f = ROOT.TFile("examples/tree.root")
In [5]: f.ls()
TFile** examples/tree.root
TFile* examples/tree.root
KEY: TTree aTree;1 tree title
In [6]: t = f.Get("aTree")
In [7]: t.Print()
******************************************************************************
*Tree :aTree : tree title *
*Entries : 1000000 : Total = 24071514 bytes File Size = 19821249 *
* : : Tree compression factor = 1,21 *
******************************************************************************
*Br 0 :normal : normal/D *
*Entries : 1000000 : Total Size= 8023900 bytes File Size = 7227246 *
*Baskets : 251 : Basket Size= 32000 bytes Compression= 1,11 *
*............................................................................*
*Br 1 :uniform : uniform/D *
*Entries : 1000000 : Total Size= 8024155 bytes File Size = 5452842 *
*Baskets : 251 : Basket Size= 32000 bytes Compression= 1,47 *
*............................................................................*
*Br 2 :var : var/D *
*Entries : 1000000 : Total Size= 8023135 bytes File Size = 7134158 *
*Baskets : 251 : Basket Size= 32000 bytes Compression= 1,12 *
*............................................................................*
In [8]: t.
Display all 326 possibilities? (y or n)

Example III - simple graphs

import ROOT

import numpy as n

x = n.linspace(0, 4*n.pi,101)

y = n.cos(x)

g = ROOT.TGraph(len(x), x,y)

g.SetTitle("cosine in x=[%.1f, %.1f]" % (x[0], x[-1]))

g.GetXaxis().SetTitle("x")
g.GetYaxis().SetTitle("y")

g.Draw("AL")

Example IV - writing treesin C++:

{
    TFile* f = new TFile("tree.root", "recreate");
    TTree* t = new TTree("aTree", "tree title");

    double n;
    double u;
    double x;

    t->Branch("normal", &n, "normal/D");
    t->Branch("uniform", &u, "uniform/D");
    t->Branch("var", &x, "var/D");

    for (int i=0; i < 1000000; ++i) {
        n = gRandom->Gaus();
        u = gRandom->Uniform();
        x = 2*u + 3 + n;
        t->Fill();
    }

    f->Write();
    f->Close();
}

in python:

#!/usr/bin/env python

import ROOT
import numpy as n

print "Writing a tree"

f = ROOT.TFile("tree.root", "recreate")
t = ROOT.TTree("name_of_tree", "tree title")


# create 1 dimensional float arrays (python's float datatype corresponds to c++ doubles)
# as fill variables
n = n.zeros(1, dtype=float)

u = n.zeros(1, dtype=float)

# create the branches and assign the fill-variables to them
t.Branch('normal', n, 'normal/D')
t.Branch('uniform', u, 'uniform/D')

# create some random numbers, fill them into the fill varibles and call Fill()
for i in xrange(100000):
    n[0] = ROOT.gRandom.Gaus()

    u[0] = ROOT.gRandom.Uniform()
    t.Fill()

# write the tree into the output file and close the file
f.Write()
f.Close()

Examples V - Drawing

In [1]: import ROOT

In [2]: f = ROOT.TFile("examples/tree.root")

In [3]: t = f.Get("aTree")

In [4]: t.Draw("uniform")

Example VI - ProcessLine

#!/usr/bin/env python
from ROOT import TTree, TFile, AddressOf, gROOT

# Make a tree
f = TFile('myTest.root','RECREATE')
t = TTree('MyTree','My test tree')

# Create a struct
gROOT.ProcessLine(\
  "struct MyStruct{\
    Int_t someInt;\
    Double_t someDouble;\

  };")

from ROOT import MyStruct

# Create branches in the tree
s = MyStruct()

t.Branch('rootInt',AddressOf(s,'someInt'),'someInt/I')
t.Branch('rootDouble',AddressOf(s,'someDouble'),'someDouble/D')

# Fill tree
for i in range(100):
  s.someInt = i

  s.someDouble = i
  t.Fill()

f.Write()

f.Close()