How to replace a numerical value in a Python list

So I got this list of lists:

lst = [[0,1],2,[3]]

and I got a list of tuples:

lst_2 = [("x1","y1"),("x2","y2"), ("x3","y3"), ("x4","y4")]

I want to replace values inside lst with the index 0 value of each of the tuples in lst_2, and the tuple taken depends on the numerical value in lst. So it becomes:

lst = [["x1","x2"], "x3", ["x4"]]

Please don’t roast me thanks so much

>Solution :

Try this:

lst = [[0,1],2,[3]]
lst_2 = [("x1","y1"),("x2","y2"), ("x3","y3"), ("x4","y4")]

res = []
for l in lst:
    if isinstance(l, list):
        res += [[lst_2[i][0] for i in l]]
    else:
        res += [lst_2[l][0]]
print(res)

Or with List Comprehensions:

res = [[lst_2[i][0] for i in l] if isinstance(l, list) else lst_2[l][0] for l in lst]

[['x1', 'x2'], 'x3', ['x4']]