Matplotlib version - - [ '1.5.2']
install Matplotlib -- auto-install through winpython 3.5

Code:

import numpy as np
import matplotlib.pyplot as plt
plt.close("all")

x = np.linspace(0.0, 2 * np.pi, 1000)
y = np.cos(2*x)

plt.polar(x, y)

Problem: Generates only 2 lobes (not 4 lobes)
Incorrect figures (generated by Matplotlib) and correct figure (by matlab) are attached

Incorrect(Matplotlib).pdf
Correct(Matlab).pdf