Python - Who can explain me this sequence?

Question

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

Answer 1

As Ramin.RX7 stated, the remove function is removing n on each iteration.
a = [1,2,3,4,5]
n:0 = a[0] which is 1
1 is removed

a = [2,3,4,5]
n:1 = a[1] which is now 3
3 is removed

a = [2,4,5]
n:3 = a[3] which is now 5
5 is removed

print(a)
[2, 4]

Answer 2

Line 2: select all members of a and name them n
Line 3: remove n from a
Line 4: print a every time we remove a member
Line 5: at the end we print a and there is nothing in it.

Answer 3

Paolo De Nictolis
Not that surprising...:

On the first round of Iteration you remove the 1. element 1(with index 0). Python prints [2,3,4,5]
Now 2 is the first element in the list (index 0).
The second round of iteration starts and n takes care of the second element in the list which is 3 (index 1) and removes it.
Then the third element 5(now Index 2) is removed.
After that No more elements with Index>2 are left.
The list hast two elements now...
2 and 4...

a=[2,4]

Answer 4

Ramin.RX7 execute this code and... SURPRISE! Result is [2,4]!

Answer 5

removing during iteration leads to computable but for humans normally surprising results.