Chapter 2 using default random() makes error

[utt54321]

While excecuting follow code:
samples = [lambda_1.random()[0] for i in range(20000)]
it shows:

Traceback (most recent call last):
  File "C:/Users/13910/PycharmProjects/untitled/rist.py", line 15, in <module>
    samples = [lambda_1.random()[0] for i in range(20000)]
  File "C:/Users/13910/PycharmProjects/untitled/rist.py", line 15, in <listcomp>
    samples = [lambda_1.random()[0] for i in range(20000)]
IndexError: too many indices for array