What does the code do?

Question

>>> a = [1, 2, 3]
>>> a[11:11]
[]
>>> a[11:11] = "xyz"
>>> a
[1, 2, 3, 'x', 'y', 'z']

Answer 1

𝓕𝓛𝓨 It's all 'bout the syntax. Slices, when assigned, actually modifies the mutable object from which the slice was made. Using the slice as a value is another matter. See:

foo = [1, 2, 3]

# 'foo' is modified coz Python was made like that, to modify the list when you're directly making assignments to it
foo[:2] = "o"

# the slice now makes a separate object in the heap because you aren't assigning to it directly, just coz the syntax is like that
print(id(foo), id(foo[:2]))

# Basically, slicing and slice assignment are two separate things. It's a feature Python has. Just some crazy syntax :)

Answer 2

Since you're doing slice assignment, the source will be treated as a sequence.
When a string is used as a sequence, each character is a separate element(character), so it gets split up and inserted into the list.
If you want to replace the slice with the whole string, wrap it in a list.
>>> a[11:11] = ["xyz"]

Hope you know why a[11:11] returns empty list []
https://www.sololearn.com/discuss/2955122/?ref=app

Answer 3

Hey!
I found the actual reason. Since, python doesn't have references, It's all about slice assignment not memory locations.
Hope it helps you.
https://stackoverflow.com/questions/10623302/how-does-assignment-work-with-list-slices

Answer 4

Simba Thanks for reply.

I don't know how to describe the question.
Maybe we can change the code to:

>>> a = [1, 2, 3]
>>> id(a[1]), id(a[1:1])
(1655224256, 17999848)

>>> a[1:1] = "xyz"
>>> id(a[1]), id(a[1:1])
(52164608, 17999848)
>>> a
[1, 'x', 'y', 'z', 2, 3]

Answer 5

Simba Thanks again.

Perhaps I'll find the answer myself by reading the source code of CPython.

>>> a = [1, 2, 3]
>>> id(a[0]), id(a[1]), id(a[2])
(1655224240, 1655224256, 1655224272)
>>> id(a[0:0]), id(a[1:1]), id(a[2:2]), id(a[11:11])
(19356136, 19356136, 19356136, 19356136)