I can't understand a behavior .index method inside for loop (Python 3.3.1 (v3.3.1:d9893d13c628, Apr 6 2013, 20:30:21) [MSC v.1600 64 bit (AMD64)] on win32)
L = [e for e in range(11)]
print(L)
for e in L[:]:
print(e, L.index(e))
L[L.index(e)] *= e
print(L)
output:
>>>
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
0 0
1 1
2 2
3 3
4 2
5 5
6 6
7 7
8 8
9 3
10 10
[0, 1, 16, 81, 4, 25, 36, 49, 64, 9, 100]
>>>
I expected the final list [0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
By the time you hit 4, your list is [0, 1, 4, 9, 4, 5, 6, 7, 8, 9, 10], having replaced the first 3 elements. .index() finds the first occurence of 4, at index 2, not 5, as you appear to be expecting. The same goes for 9; you already replaced 3 with 9 earlier in the loop and L.index(9) returns 3 instead of 10.
Don't use list.index() on a changing list; use enumerate() instead:
L = [e for e in range(11)]
print(L)
for i, e in enumerate(L[:]):
print(e, i)
L[i] *= e
print(L)
which then results in:
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
0 0
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
10 10
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
You can replace [e for e in range(11)] with a simple list(range(11)). And you can replace your whole script with:
[e * e for e in range(11)]
