My test expression in if statement increases with the input

I am trying to append a "P(i)" and a "D(i)" for every i.

li = []
        for i in range(n):
            li.append(f"p{i+1}")
            li.append(f"d{i+1}")

Now, I am finding all the ways in which the list could be arranged such that for every i, P(i) always occurs before D(i)

perm = permutations(li)

For smaller n values, such as 2 or 3, I could just write:

k = list(perm)
    for j in k:
        if j.index("p1")<j.index("d1") and j.index("p2")<j.index("d2"):
            count += 1

But for higher n values, in this way I will have to write expression starting from p1 to pn, which obviously isn't something I want to do.

In cases like these, where my test expression increases with the input, what should I do?