code: def plot_ts(fignum, dates, ts):
      
      vertical_plot_init(fignum, 10, 3)
      TS, Chrons = pmag.get_ts(ts)
      p = 1
      X, Y = [], []
      for d in TS:
          if d <= dates[1]:
              if d >= dates[0]:
                  if len(X) == 0:
                      ind = TS.index(d)
                      X.append(TS[ind - 1])
                      Y.append(p % 2)
                  X.append(d)
                  Y.append(p % 2)
                  p += 1
                  X.append(d)
                  Y.append(p % 2)
          else:
              X.append(dates[1])
              Y.append(p % 2)
              plt.plot(X, Y, 'k')
              plot_vs(fignum, dates, 'w', '-')
              plot_hs(fignum, [1.1, -.1], 'w', '-')
              plt.xlabel("Age (Ma): " + ts)
              isign = -1
              for c in Chrons:
                  off = -.1
                  isign = -1 * isign
                  if isign > 0:
                      off = 1.05
                  if c[1] >= X[0] and c[1] < X[-1]:
                      plt.text(c[1] - .2, off, c[0])
              return
docs: plot the geomagnetic polarity time scale
  
      Parameters
      __________
      fignum : matplotlib figure number
      dates : bounding dates for plot
      ts : time scale ck95, gts04, or gts12