スライス操作（きりとり）

  0     1     2     3     4     5     6
 [0:]  [1:]  [2:]  [3:]  [4:]  [5:]  [6:] 
  +-----+-----+-----+-----+-----+-----+
  |  P  |  y  |  t  |  h  |  o  |  n  |
  +-----+-----+-----+-----+-----+-----+
[-6:] [-5:] [-4:] [-3:] [-2:] [-1:]
 -6    -5    -4    -3    -2    -1 


>>> w
'Python'
>>> len(w)
6
>>> type(w)
<class 'str'>
>>> w[:]
'Python'
>>>
>>> w[3]
'h'
>>> w[0]
'P'
>>> w[-3]
'h'
>>>
>>> w[2:]
'thon'
>>> w[-4:]
'thon'
>>>
>>> w[:2]
'Py'
>>> w[:-4]
'Py'
>>>