Python challenge question

Question

Why this code doesn't remove all the items from the list?
a=[1,2,3,4,5]
for x in a:
a.remove(x)
print(a)

When i run this i get [2,4] instead of an empty list but i just don't get it why 2 and 4 are left.
When i do this
a=[1,2,3,4,5]
for x in a:
print(x)
then the output is 1 2 3 4 5 so x can take all these values but still the list is not getting empty????
Damn confusing!!!

Answer 1

The problem for this behaviour is really simple. Let's go through step by step or in other words iteration for iteration.
you started with:

a=[1,2,3,4,5]
for x in a
a.remove(x)
print(a)

1. iteration:
for loop gives you index 0 from a => "1"
then you remove(x) = "1" from list a
list a is now [2,3,4,5]

2. iteration:
for loop gives you now index 1 from a => "3"
then you remove 3 from the list a
list a is now [2,4,5]

3. iteration:
for loop gives you now index 2 from a => "5"
then you remove 5 from the list a
list a is now [2,4]

As there are no more elements iteration stops here. To get rid of this problem you have to start iteration from the end of the list with: [::-1]. This code is doing this:

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

https://code.sololearn.com/cQGiLQHt6TEL/?ref=app

Answer 2

Because there is an invisible counter in "for x in a" it counts from 0 "i = 0", in each iteration it gets incremented by 1 "i += 1" and gives variable a new value "x = a[i]". It repeates this, until there are no values at "a[i]", because at the third iteration "i = 3" and "a = [2, 4], there are no values at "a[i]" = "a[3]", for loop is broken.

>>>a = [1, 2, 3, 4, 5]
>>>for x in a:
... a.remove(x)
... print(a)
...
[2, 3, 4, 5]
[2, 4, 5]
[2, 4]
>>>print(a)
[2, 4]

Answer 3

Lothar and Seb TheS thanks a lot for the explanation 👍

Answer 4

Excel why x=odd?

Answer 5

Excel I don't understand what u r saying.
Can u please explain

Answer 6

X=odd

Answer 7

No item was assigned to remove.
So odd or random