Create a function that rearranges item in list and shifts the other items (Python)

Question

I'm trying to write a function in Python that would re-arrange specified item, moved it to new position and the other items would shift in relation.

The function accepts two arguments:

old_index - current index of item new_index - index where we want the item to be moved

Let's say I have this list:

list = ['a', 'b', 'c', 'd', 'e', 'f', 'g']

I decide to move letter 'f' before letter 'b'. This means old_index = 5 and new_index = 1 . After this operation is done, I want the letters to be shifted, not swapped, resulting in this:

list = ['a', 'f', 'b', 'c', 'd', 'e', 'g']

I've come up with following function:

def shift_letters(old_index, new_index):

    shifted = list.index(list[old_index])
    selected = list[old_index]
    print 'selected', selected
    list.insert(new_index, selected)
    print 'inserted %s at %s' % (selected, new_index)
    if old_index < new_index:
        removed = list.pop(shifted - 1)
    else:
        removed = list.pop(shifted + 1)

    print 'removed %s' % removed

But that doesn't work very well. I'd like to avoid making copies of the list if possible (lists in my application could be very large).

Answer 1

Pop from the old index, insert at the desired index.

>>> mylist = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> old_index = 5
>>> new_index = 1
>>> 
>>> mylist.insert(new_index, mylist.pop(old_index))
>>> mylist
['a', 'f', 'b', 'c', 'd', 'e', 'g']

Answer 2

def shift_letters(list, old_index, new_index):
  value = list.pop(old_index)
  list.insert(new_index, value)

Answer 3

So maybe:

ls.insert(new, ls.pop(old)) ?