如何迭代python列表？

Question

If I execute this code, the following error message occurs:

IndexError: list index out of range python

def reverse_invert(lst):
    inverse_list = []

    for i in lst:
        if isinstance( i, int ):
             inverse_list.append(lst[i])
        #print(inverse_list)       
             print(i)       
        else:
            break
    return inverse_list

Why is it?

Answer 1

for i in lst:

will iterate the elements of lst .

If you want to iterate indexes , use

for i in range(len(lst)):

If you want both the element and the index, use enumerate :

for i, el in enumerate(lst):

Answer 2

You are iterating the elements of list but trying to use the element as index. You should change your code like this:

def reverse_invert(lst):
inverse_list = []

for i in lst:
    if isinstance( i, int ):
         inverse_list.append(i) # changed this one.
    #print(inverse_list)       
         print(i)       
    else:
        break
return inverse_list

Answer 3

List comprehension would work fine:

a = [1, 'a', 2, 3]

print [d for d in a[::-1] if isinstance(d, int)]

And if you want to reverse it just tiny change would do:

a = [1, 'a', 2, 3]

print [d for d in a[::-1] if isinstance(d, int)]

Or maybe I missed your point.

Answer 4

Generally it means that you are providing an index for which a list element does not exist.

Eg, if your list was

[1, 3, 5, 7], and you asked for the element at index 10, you would be well out of bounds and receive an error, as only elements 0 through 3 exist.