import math

import numpy as np
import ROOT

CPol = ROOT.TCanvas("CPol", "TGraphPolar Examples", 500, 500)

rmin = 0
rmax = math.pi * 2
r = np.array([])
theta = np.array([])

fp1 = ROOT.TF1("fplot", "cos(x)", rmin, rmax)
for ipt in range(1000):
    r = np.append(r, ipt * (rmax - rmin) / 1000 + rmin)
    theta = np.append(theta, fp1.Eval(r[ipt]))

grP1 = ROOT.TGraphPolar(1000, r, theta)
grP1.SetTitle("")
grP1.SetLineColor(2)
grP1.Draw("AOL")