Fibonacci Series Using Lists?

Python's range starts at 0, you need to start with generating element 2. By starting at 0, you get negative indices for the first couple of calculations, which access from the end of the list. To fix this, change the loop to for i in range(2, 8).

To clarify what seems to be a source of confusion, by starting the range at zero and using negative indexing you end up with the following terms being summed and appended to the list:

f[2] = f[0-1] + f[0-2] = f[-1] + f[-2] (= f[1] + f[0]) = 1 + 1 = 2  # looking good
f[3] = f[1-1] + f[1-2] = f[0] + f[-1] (= f[0] + f[2]) = 1 + 2 = 3   # looking good
f[4] = f[2-1] + f[2-2] = f[1] + f[0] = 1 + 1 = 2                    # oops!
f[5] = f[3-1] + f[3-2] = f[2] + f[1] = 2 + 1 = 3

From that point on the numbers are on track, but offset from the proper indexing by 2.

f=[1,1]

for i in range(8):
    f.append(f[i]+f[i+1])

print(f)

RESULT

[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

f=[1,1]
for i in range(8):
    s=len(f)
    f.append(f[s-1]+f[s-2]) #sum of last two elements

print(f)

or use -1 and -2 as index for two last element.

Adding to pjs' answer: When i = 0, you are adding f[-1] and f[-2], where an index of -1 gives you the last element in the list and so on.

To fix that, as other answers have already pointed out, you need to set the correct starting point for range().

You should be aware that the range function starts at 0 if you don't explicitly specify a starting point. In your case, it should be: for i in range(2, 8).

Output:

[1, 1, 2, 3, 5, 8, 13, 21]

Also, in Python, you can use negative index in an array to count from the right instead of the left, this is why you had this weird result.

Script

f=[1,1]

for i in range(2,8):
  print(i)
  f.append(f[i-1]+f[i-2])
  print(f)

Output

2
[1, 1, 2]
3
[1, 1, 2, 3]
4
[1, 1, 2, 3, 5]
5
[1, 1, 2, 3, 5, 8]
6
[1, 1, 2, 3, 5, 8, 13]
7
[1, 1, 2, 3, 5, 8, 13, 21]

Issue is i starts from 0, f[-1], f[-2] returns 0. start using range from 2 and 8 represents first 8 fibonacci numbers.

removing debug print

Script

f=[1,1]

for i in range(2,8):
   f.append(f[i-1]+f[i-2])
print(f)