Python implements the method of naming slices

The content of this article is about the method of naming slices in Python. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Requirements

Our code has become unreadable, with hard-coded slice indexes everywhere, and we want to optimize them.

2. Solution

If there are many hard-coded index values ​​​​in the code, it will lead to poor readability and maintainability.

The built-in slice() function creates a slice object that can be used anywhere where slicing operations are performed.

items=[0,1,2,3,4,5,6]
a=slice(2,4)
print(items[2:4])
print(items[a])

items[a]=[10,11,12,13]
print(items)

del items[a]
print(items[a])
print(items)

Running result:

[2, 3]
[2, 3]
[0, 1, 10, 11, 12, 13, 4, 5, 6]
[12, 13]
[0, 1, 12, 13, 4, 5, 6]

If there is an instance s of the slice object. Information about the object can be obtained through the s.start, s.stop and s.step properties respectively. For example:

items=[0,1,2,3,4,5,6]
a=slice(2,8,3)
print(items[a])
print(a.start)
print(a.stop)
print(a.step)

Result:

[2, 5]
2
8
3

Additionally, slices can be mapped onto sequences of specific sizes by using the indices(size) method. This will return a (start, stop, step) tuple, all values ​​have been properly restricted within the bounds (to avoid IndexError exceptions when doing index operations), for example:

s='HelloWorld'
a=slice(2,5)
print(a.indices(len(s)))
for i in range(*a.indices(len(s))):
    print(str(i)+":"+s[i])

Result:

(2, 5, 1)
2:l
3:l
4:o

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