Invalid syntax in "for item in L" loop

You are missing a closing parenthesis on the line before:

      L = primes(int(math.sqrt(perimeter)) #list of primes to divide the perimeter
#               ^   ^         ^         ^^
#nesting count  1   2         3         21

See how we don't reach 0 in the "nesting count" below the line?

You're missing a parenthesis:

L = primes(int(math.sqrt(perimeter)))
                                    ^
                                    |
                                 this one

This happens to me all the times, you just needed look at the line before.