old_contents: #!/usr/bin/env python3
  # -*- coding: utf-8 -*-
  
  import numpy as np
  import matplotlib.pyplot as plt
  
  # Build datas ###############
  
  t = np.linspace(0, 2. * np.pi, 200)
  
  x = 0.7 * np.sin(t) * np.sin(3. * t)
  y = 0.7 * np.cos(t) * np.sin(3. * t)
  
  # Plot data #################
  
  fig = plt.figure(figsize=(8.0, 8.0))
  ax = fig.add_subplot(111)
  
  ax.plot(x, y)
  
  ax.set_xlim([-0.8, 0.8])
  ax.set_ylim([-0.8, 0.8])
  
  # Save file and plot ########
  
  plt.savefig("parametric_curve.png")
  
  plt.show()
  
  
new_contents: #!/usr/bin/env python3
  # -*- coding: utf-8 -*-
  
  import numpy as np
  import matplotlib.pyplot as plt
  
  # Build datas ###############
  
  t = np.linspace(0, np.pi, 200)
  
  x = 0.7 * np.sin(t) * np.sin(3. * t)
  y = 0.7 * np.cos(t) * np.sin(3. * t)
  
  # Plot data #################
  
  fig = plt.figure(figsize=(8.0, 8.0))
  ax = fig.add_subplot(111)
  
  ax.plot(x, y)
  
  ax.set_xlim([-0.8, 0.8])
  ax.set_ylim([-0.8, 0.8])
  
  # Save file and plot ########
  
  plt.savefig("parametric_curve.png")
  
  plt.show()
  
  
subject: Fix a mistake.