From within the Python interpreter:

>>> set('hellohellohello')
{'h', 'o', 'l', 'e'}
>>> set(['hellohellohello'])
{'hellohellohello'}
>>> set(('hellohellohello'))
{'h', 'o', 'l', 'e'}
>>> set(('hellohellohello',))
{'hellohellohello'}
>>> set(('hello', 'hello', 'hello'))
{'hello'}
>>> set(('hello', ('hello', 'hello')))
{'hello', ('hello', 'hello')}
>>> set(('hello', ['hello', 'hello']))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

Note the difference between initializing a set with a list of objects and attempting to add a list as an object in a set.