py3

for cls in object.__subclasses__(): 
    cls = choice(object.__subclasses__())

Traceback (most recent call last):
  File "source_file.py", line 2, in <module>
    cls = choice(object.__subclasses__())
NameError: name 'choice' is not defined

py3

from random import choice
for cls in object.__subclasses__(): 
    cls = choice(object.__subclasses__())

py3

from random import choice
for cls in object.__subclasses__(): 
    cls = choice(object.__subclasses__())
print(int())
print(dict())
print(set())
print(list())

0
{}
set()
[]