This is nicely structured but I would change the variable name from ret to something more meaningful

This is clever indeed but also makes the code too vague

This is actually clever, well done!

here are few examples to simplify it:
map(int, a) --> apply int to every list object in list a to make them integers
map(str, a) --> apply str to every list object in list a to make them strings

Its nice to see this type of solution where the its "opened up" with empty list and normal for loop. There's a lot of solutions with lambda and comprehension (one liners) but these dont add that much value to real life scenarios when the talking point is maintanability. :)