What does ::-1 stand for in python?

In Python: :-1 means outputting characters or numbers in reverse order. For example, when line = "abcde", use the statement line[::-1], and the final running result is: 'edcba'. Please see the detailed explanation below.

1. Reverse

::-1 involves outputting numbers or characters in reverse order

2. Detailed explanation

1. i: j

a = [0,1,2,3,4,5,6, 7,8,9]
b = a[i:j] means copying a[i] to a[j-1] to generate a new list object
b = a[1:3] Then, The content of b is [1,2]
When i defaults, the default is 0, that is, a[:3] is equivalent to a[0:3]
When j defaults, the default is len(alist ), that is, a[1:] is equivalent to a[1:10]
When i and j are both default, a[:] is equivalent to a complete copy of a

For example:

line = "abcde"
line[:-1]
The result is: 'abcd'

2, ::- 1

b = a[i:j:s] In this format, i and j are the same as above, but s represents step, and the default is 1.
So a[ i:j:1] is equivalent to a[i:j]
When s<0, when i is defaulted, the default is -1. When j is defaulted, the default is -len(a)-1
So a[::-1] is equivalent to a[-1:-len(a)-1:-1], that is, copying from the last element to the first element. So you see something in reverse order.

For example:

line = "abcde"
line[::-1]
The result is: 'edcba'
line [:-1] is actually the remaining part after removing the last character (newline character) of this line of text.

In fact, the problem is not difficult. It will be very clear if you run it yourself.

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