import ROOT

ROOT.gROOT.SetStyle("Plain")
rndm = ROOT.TRandom3()
rndm.SetSeed(123456)

f1 = ROOT.TF1("f1", "pol0")
chi2 = ROOT.TH1D("chi2", "Chi2 Prob", 100, 0, 1)
chi2.SetMinimum(0)
for j in range(1, 1000):
  h1 = ROOT.TH1D("h1", "rnd", 10, 0, 1)
  for i in range(0, 1000):
    h1.Fill(rndm.Uniform())
  h1.Fit(f1, "Q0")
  chi2.Fill(ROOT.TMath.Prob(f1.GetChisquare(), f1.GetNDF()))
  h1 = None
c = ROOT.TCanvas()
chi2.Draw()
c.SaveAs("02-chi2.pdf")