Python: keep track of elements moving within a list

Question

I have a list of objects:

MyList = [A, B, C, D, E, F, G]

During the execution of the code, these objects might be moved of position. This movement usually happens one-by-one, so (for example) the item "D" might be moved right after "A". The list becomes, hence, as follows:

MyList = [A, D, B, C, E, F, G]

What I would like to know is if there's a method (I've already tried to build an algorithm but I would like to make the code shorter) to keep track of the elements over the list, so that I can use the indexes to recover them into the same list when I need to use them (the other parts of the code cannot be touched, otherwise I would implement this in the moving loops themselves). To explain better, I would like to know if it's possible to make something like this:

#ORIGINARY LIST
MyList = [A, B, C, D, E, F, G]
Current_Indexes= [0,1,2,3,4,5,6]

#ITERATION THAT MOVES D RIGHT AFTER A
MyList = [A, D, B, C, E, F, G]
Current_Index_Mapping = [0,3,1,2,4,5,6] #method or built-in function??? 

I have in mind something algorithmically, like creating a list at the beginning of the code like this:

for i in range(0, len(MyList)):
    Current_Index_Mapping.append((i,MyList[i]))

and then extracting the tuples to update the Current_Index_Mapping list. However I'm pretty new to Python programming and I don't know lot of methods and built-in functions, so I was wondering: does anyone have a better idea to get the same result?

Answer 1

Map the id of objects to original indice:

>>> a, b, c, d, e, f, g = [object() for i in range(7)]
>>> lst = [a, b, c, d, e, f, g]

>>> objid_to_idx = {id(obj): idx for idx, obj in enumerate(lst)} # <---
# {
#     id(a): 0,
#     id(b): 1,
#     ...
#     id(g): 6,
# }

>>> [objid_to_idx[id(obj)] for obj in lst]
[0, 1, 2, 3, 4, 5, 6]

>>> lst = [a, d, b, c, e, f, g]
>>> [objid_to_idx[id(obj)] for obj in lst]
[0, 3, 1, 2, 4, 5, 6]

>>> lst = [a, d, b, a, c, e, e, f, g]
>>> [objid_to_idx[id(obj)] for obj in lst]
[0, 3, 1, 0, 2, 4, 4, 5, 6]

used dict comprehension, enumerate to build mapping.