# metoda append vrací None
>>> xs = []
>>> a = xs.append(1)
>>> a
>>> print(a)
None

# neexistující výřez nezhavaruje
>>> xs = 'ahoj'
>>> xs[3]
'j'
>>> xs[4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range
>>> xs[3:]
'j'
>>> xs[4:]
''