Python: For loop list gives IndexError

Question

a = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
for i in a:
 print(a[i])
IndexError: list index out of range

I don't undertand why I get this error.

• JohanL: for i in a: is iterating over the elements of a not the indexes. Thus, you are using the elements themselves as indexes into the list.
• Chipmunkafy: @JohanL How can I iterate over the indexes?
• JohanL: for i, e in enumerate(a): will give both the index and the value.
• JohanL: @davedwards As long as the element is not repeating.
• JohanL: Yes, that is true, i is the index and e is the element (or value).

Answer 1

You are referencing the value not the index. Try:

for i in range(len(a)):
 print(a[i])

Answer 2

You don't actually need an index in the example you give, since you are only printing the values of the items in the list, in which case printing the items directly would suffice:

for i in a:
 print(i)

Answer 3

If you want the index of an element, it is possible to enumerate the data in the array, using

for i, e in enumerate(a):
 print(a[i]) # assuming this is just a placeholder for a more complex instruction

gives what you want, where i is the index and eis the (value of) the element in the list. But often you do not need the index since you want to use the value of the element directly. In those cases it is better to do just

for e in a:
 print(e)