You get some nested lists. Keeping the original structures, sort only elements (integers) inside of the lists. In other words, sorting the intergers only by swapping their positions. 
```
Example
Input   : [[[2, 1], [4, 3]], [[6, 5], [8, 7]]]
Output  : [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]
```
Note:
The structures of the lists are regular (symmetrical) and their depths are 3.
import re
def sort_nested_list(arr):
    s=str(arr); ns=sorted(re.findall(r"\d+",s),key=int,reverse=True)
    return eval(re.sub(r"\d+",lambda _:ns.pop(), s))
import re
def sort_nested_list(arr):
    s=str(arr); ns=sorted(re.findall(r"\d+",s),key=int,reverse=True)
    return eval(re.sub(r"\d+",lambda _:ns.pop(), s))