How is this working, I mean how is python executing

Question

a = [0,1,2,3]

for a[-1] in a:
print(a[-1])

https://code.sololearn.com/cs2mWY3hjmOs/?ref=app

Answer 1

https://code.sololearn.com/c2kNMIGR1HCC/?ref=app

Answer 2

The for loop works like this:
for A in B:
-> Get the elements from B one at a time and assign that value to A. A is a[-1] in your code, so the value gets assigned to the last element of a.

Change the output to this:
print(a)
Then you can see the whole list in each iteration and see that only the last item changes.
In the last step a[-1] is 2 from the previous step and gets assigned to itself, so output is 2 again

Answer 3

KishanBGajera take this modification of your code, it prints the complete list in the loop and the list is longer:

a = [0,1,2,3,4,5]
for a[-1] in a:
print(a)

Output is
[0,1,2,3,4,0]
[0,1,2,3,4,1]
[0,1,2,3,4,2]
[0,1,2,3,4,3]
[0,1,2,3,4,4]
[0,1,2,3,4,4]

As you can see only the last element (a[-1]) changes. It is set by the loop.

Read the loop like this: set a[-1] to each of the elements in a (one at a time) and run the code inside the loop

Answer 4

Benjamin Jürgens please elaborate I'm not getting it 😕

Answer 5

Benjamin Jürgens thanks 👍

Answer 6

Sayed🇧🇩🇧🇩 thanks 👍

Answer 7

It is a slicing
Last element (a[-1]) because you have given in the range
And your print a[-1] that is 2 and it will be assigned to itself so output is showing:-
0
1
2
2
Try-
a = [0,1,2,3]
for a[-1] in a:
print(a[-1], end="")

Answer 8

a = [0,1,2,3]
for i in a:
pass
print(i)
# everytime loop runs i is assigned corresponding value of list a from 0 index to -1 index . so it's final value is 3

a = [0,1,2,3]
for a[-1] in a:
print(a[-1])
# now consider same case with this one too .
# first iteration a[-1] = a[0] = 0
# 2nd iteration a[-1] = a[1] = 1
# 3rd iteration a[-1] = a[2] = 2

# 4th iteration a[-1] = a[3] which is a[-1] actually . in 3rd iteration a[-1] was assigned value 2 . so this time a[-1] = a[3] = a[-1] =2
#by Nicolaus Copernicus

Answer 9

Thanks Nicolaus easily explained this problem👍