3 Minutes Python | Slice
What is slice and how we can use it to handle list/tuple/string?
What is slice?
Slice is one of the most common operations in python. It can be applied on Tuple, List or String. Its common form is [start:stop:step]. Start defaults to be 0, stop defaults to be the length of the list/tuple/string, and step defaults to be 1.
Note that slice operation does not do in-place change, meaning that it will not change the object on which it is applied.
Examples:
1. Slice can be used to get part of a list/tuple/string
example_lst = [1, 2, 3, 4, 5]
example_str = 'abcde'
example_tupl = (1, 2, 3, 4, 5)# new_lst_1 now evaluates as [2, 3, 4, 5]
new_lst_1 = example_lst[1:]# new_lst_2 now evaluates as [1, 2, 3]
new_lst_2 = example_lst[:3]# new_lst_3 now evaluates as [2, 3]
new_lst_3 = example_lst[1:3]# new_str now evaluates as 'bc'
new_str = example_str[1:3]
# new_tupl now evaluates as (2, 3)
new_tupl = example_tupl[1:3]
2. Slice can be used to get a reversed list/tuple/string
example_lst = [1, 2, 3, 4, 5]# new_lst now evaluates as [5, 4, 3, 2, 1]
new_lst = example_lst[::-1]
3. Slice can be used to copy a new list/string/tuple. This can be useful since it’s doing a deep copy of the list. This means with the new copied list, we can change it without affecting the old list.
example_lst = [1, 2, 3, 4, 5]# new_lst now evalutes as [1, 2, 3, 4, 5]
new_lst = example_lst[:]# example_lst is still [1, 2, 3, 4, 5]
new_lst[0] = -99# lst_ref now also evaluates as [1, 2, 3, 4, 5]
lst_ref = example_lst# example_lst now changes to [-99, 2, 3, 4, 5]
lst_ref[0] = -99
4. Slice can be used to get part of a list on an interval
example_lst = [1, 2, 3, 4, 5, 6, 7]# new_lst now evaluates as [1, 3, 5, 7]. It will starts from the
# first element at position 0, and then get the element at
# position 0+2 = 2, and then stops at the last element before
# position 7.
new_lst = example_lst[0:7:2]
5. Slice operation returns another list/tuple/string corresponding to the type that it is applied to. And thus, we can do an operation chain on the sliced object.
example_lst = [1, 2, 3, 4, 5, 6, 7]# new_lst now evaluates as [5, 4, 3, 2]. The following operation
# first sliced [1:5], and it returns [2, 3, 4, 5]. And then
# it is applied reverse [::-1], which is essentially
# [2, 3, 4, 5][::-1], and this gives us [5, 4, 3, 2].new_lst = example_lst[1:5][::-1]
RECAP
This post summarized some functionalities of python slice. Slice is usually in the form of [start:stop:step]. It’s used on list/tuple/string. The operation returns another list/tuple/string and does not change the original object.
We can use slice to get part of list/string/tuple or to reverse it. We can also do a chain slice operation on a list/string/tuple as well.
