old_contents: from Numeric import *
  from pl import *
  
  # main
  # 
  # Illustration of logarithmic axes, and redefinition of window.
  
  def main():
  
      plfont(2)
      plot1(0)
      plot1(1)
  
      # Restore defaults
      plfont(1)
      plcol0(1)
      
      plend()
  
  def plot1(type):
  
      pladv(0)
      f0 = 1.0
      freql = -2.0 + arrayrange(101)/20.0
      freq = pow(10.0, freql)
      ampl = 20.0 * log10(1.0 / sqrt(1.0 + pow((freq / f0), 2.)))
      phase = -(180.0 / pi) * arctan(freq / f0)
  
      plvpor(0.15, 0.85, 0.1, 0.9)
      plwind(-2., 3.0, -80.0, 0.0)
      plcol0(1)
      if type == 0:
  	plbox("bclnst", 0.0, 0, "bnstv", 0.0, 0)
      elif type == 1:
  	plbox("bcfghlnst", 0.0, 0, "bcghnstv", 0.0, 0)
      else:
  	print "error: type must be either 0 or 1"
      plcol0(2)
      plline(freql, ampl)
      plcol0(1)
      plptex(1.6, -30.0, 1.0, -20.0, 0.5, "-20 dB/decade")
  
      # Put labels on
      plcol0(1)
      plmtex("b", 3.2, 0.5, 0.5, "Frequency")
      plmtex("t", 2.0, 0.5, 0.5, "Single Pole Low-Pass Filter")
      plcol0(2)
      plmtex("l", 5.0, 0.5, 0.5, "Amplitude (dB)")
  
      # For the gridless case, put phase vs freq on same plot
      if type == 0:
          plcol0(1)
  	plwind(-2.0, 3.0, -100.0, 0.0)
  	plbox("", 0.0, 0, "cmstv", 30.0, 3)
  	plcol0(3)
  	plline(freql, phase)
  	plcol0(3)
  	plmtex("r", 5.0, 0.5, 0.5, "Phase shift (degrees)")
  
  main()
  
new_contents: from Numeric import *
  from pl import *
  
  # main
  # 
  # Illustration of logarithmic axes, and redefinition of window.
  
  def main():
  
      plfont(2)
      plot1(0)
      plot1(1)
  
      # Restore defaults
      plfont(1)
      plcol0(1)
      
  def plot1(type):
  
      pladv(0)
      f0 = 1.0
      freql = -2.0 + arrayrange(101)/20.0
      freq = pow(10.0, freql)
      ampl = 20.0 * log10(1.0 / sqrt(1.0 + pow((freq / f0), 2.)))
      phase = -(180.0 / pi) * arctan(freq / f0)
  
      plvpor(0.15, 0.85, 0.1, 0.9)
      plwind(-2., 3.0, -80.0, 0.0)
      plcol0(1)
      if type == 0:
  	plbox("bclnst", 0.0, 0, "bnstv", 0.0, 0)
      elif type == 1:
  	plbox("bcfghlnst", 0.0, 0, "bcghnstv", 0.0, 0)
      else:
  	print "error: type must be either 0 or 1"
      plcol0(2)
      plline(freql, ampl)
      plcol0(1)
      plptex(1.6, -30.0, 1.0, -20.0, 0.5, "-20 dB/decade")
  
      # Put labels on
      plcol0(1)
      plmtex("b", 3.2, 0.5, 0.5, "Frequency")
      plmtex("t", 2.0, 0.5, 0.5, "Single Pole Low-Pass Filter")
      plcol0(2)
      plmtex("l", 5.0, 0.5, 0.5, "Amplitude (dB)")
  
      # For the gridless case, put phase vs freq on same plot
      if type == 0:
          plcol0(1)
  	plwind(-2.0, 3.0, -100.0, 0.0)
  	plbox("", 0.0, 0, "cmstv", 30.0, 3)
  	plcol0(3)
  	plline(freql, phase)
  	plcol0(3)
  	plmtex("r", 5.0, 0.5, 0.5, "Phase shift (degrees)")
  
  main()
  
subject: Remove plend that is not appropriate for grouped plots (as in pythondemos.py) and which was therefore messing things up.