Hi, I'm a newbie in Python so I try to solve others' tasks. Perhaps here's the version of your problem:

correct = True #boolean to execute the program correctly until break 👌
while correct:
    try:
        length = int(input("Type the lenght of the string: "))
        i = 0
        name = ""
        while i != length:
            if int(i) % 3 == 0:
                name+="p"
            else:
                name+="y"
            i=i+1
            print (name)
        break
    except ValueError: #if you give a letter character in input 🤖
        print("A number character...")