python bifurcation chaos equation

MyCode

Taking advantage of the bifurcation equation I am trying to create an algorithm that produces random numbers for real in python. I keep getting this error, how can I solve it?

   import matplotlib.pyplot as plt

   def x(s,r):
         a = []
         a.append(10)
         for t in range(2,1000):
             a.append( r*x(a[t-1],r)*(1-x(a[t-1],r)))
   return plt.plot(a, t)

   x(1, 4)