Describes the _ getitem _ method in Python and slice object slicing operations,

Describes the _ getitem _ method in Python and slice object slicing operations,

Although the Fib instance can act on a for loop, it looks a little like a list, but it still cannot be used as a list, for example, taking 5th elements:

>>> Fib()[5]Traceback (most recent call last): File "<stdin>", line 1, in <module>TypeError: 'Fib' object does not support indexing

To retrieve elements by subscript like list, the _ getitem _ () method must be implemented:

class Fib(object):  def __getitem__(self, n):    a, b = 1, 1    for x in range(n):      a, b = b, a + b    return a

Now, you can access any of the series by Subscript:

>>> f = Fib()>>> f[0]1>>> f[1]1>>> f[2]2>>> f[3]3>>> f[10]89>>> f[100]573147844013817084101

Slice object and _ getitem __

You can set the _ getitem _ method to make the instance of the class use the subscript like the list. For example:

class _List(object):  def __getitem__(self, key):    print keyl = _List()l[3]  # print 3

However, if you want to use the slice operation

l[1:4] # print slice(1, 4, None)

A slice object is created for slicing. You can view the specific operation through help (slice.

a = slice(1, 4, None)range(5)[a] # print [1, 2, 3]

Richer operations

class _List(object):    def __init__(self, _list):    self._list = _list  def __getitem__(self, key):    if isinstance(key, int):      return self._list[key]    elif isinstance(key, slice):      reutrn self.__class__(self._list[key])if __name__ == '__main__':  c = _List(range(10))  b = c[1:5]  print b[3] # print 4

If the key is an integer, the list element is returned. If the key is an slice object, an instance is created and a result is returned.