How assignment works with Python list slice?

Question

Python doc says that slicing a list returns a new list.
Now if a "new" list is being returned I\'ve the following questions related to "Assignment to sl

Answer 1

When you specify a on the left side of the = operator, you are using Python's normal assignment, which changes the name a in the current context to point to the new value. This does not change the previous value to which a was pointing.

By specifying a[0:2] on the left side of the = operator, you are telling Python you want to use Slice Assignment. Slice Assignment is a special syntax for lists, where you can insert, delete, or replace contents from a list:

Insertion:

>>> a = [1, 2, 3]
>>> a[0:0] = [-3, -2, -1, 0]
>>> a
[-3, -2, -1, 0, 1, 2, 3]

Deletion:

>>> a
[-3, -2, -1, 0, 1, 2, 3]
>>> a[2:4] = []
>>> a
[-3, -2, 1, 2, 3]

Replacement:

>>> a
[-3, -2, 1, 2, 3]
>>> a[:] = [1, 2, 3]
>>> a
[1, 2, 3]

Note:

The length of the slice may be different from the length of the assigned sequence, thus changing the length of the target sequence, if the target sequence allows it. - source

Slice Assignment provides similar function to Tuple Unpacking. For example, a[0:1] = [4, 5] is equivalent to:

# Tuple Unpacking
a[0], a[1] = [4, 5]

With Tuple Unpacking, you can modify non-sequential lists:

>>> a
[4, 5, 3]
>>> a[-1], a[0] = [7, 3]
>>> a
[3, 5, 7]

However, tuple unpacking is limited to replacement, as you cannot insert or remove elements.

Before and after all these operations, a is the same exact list. Python simply provides nice syntactic sugar to modify a list in-place.