Splitting string to individual characters using slicing

Question

I'm confused how the following python code works to split a string to individual characters using b[:0] = a. Shouldn't it be just b = ['abc']?

a='abc'
b=[]
b[:0]=a
print(b)

output:

b=[a,b,c]

[Multiple explanations here](https://stackoverflow.com/questions/10623302/how-assignment-works-with-python-list-slice) in particular answer by Casey Kuball. — DarrylG, Apr 29 '20 at 08:21
@aderchox The question is more about why the piece of code behaves so — Rajarishi Devarajan, Apr 29 '20 at 08:21

score 2 · Accepted Answer · edited Apr 29 '20 at 08:26

2

This is because the list constructor can be used to split any iterables, such as strings.

You do not even need [:0],

list(a) # ['a', 'b', 'c']

or,

b = []
b[:] = a # ['a', 'b', 'c']

edited Apr 29 '20 at 08:26

Rajarishi Devarajan

581
4
14

answered Apr 29 '20 at 08:25

b-fg

3,959
2
28
44

score 1 · Answer 2 · answered Apr 29 '20 at 08:27

According to Python Doc whenever left side of assignment statement is slicing, python do __setitem__ so in this case it put right side items in the beginning of slicing. take a look at this example:

>>> a = [1,2,3,4]
>>> b = [5,6,7,8]
>>> b[3:5] = a
>>> print(b)
[5, 6, 7, 1, 2, 3, 4]

score 0 · Answer 3 · answered Apr 29 '20 at 08:32

It's two things at play here

When you do

b[:0] = <something>

The something is inserted to the beginning of the list (This is appending to a list slice)

If you did

b[1:3] = ['a', 'b', 'c']

Then the items at index 1 and 2 are replaced by the items on the right

Try the following:

b = []
b[:0] = [1, 2, 3]

You will notice the items on the right inserted to the beginning of the list

Now when you do

b[:0] = "abc"

Since the items on the right hand side have to be a sequence, the string gets unpacked to ['a', 'b', 'c'] and then these are inserted to the beginning of the list

Splitting string to individual characters using slicing

3 Answers3