while True:
    try:
        num1 = int(input("Type in the first parameter: "))
        num2 = int(input("Type in the second parameter: "))
        num3 = int(input("Type in the third parameter: "))
        break
    except ValueError:
        print("You have to type in a number. ")

while True:

    if num1 > num2 and num1 > num3:

        c = num1
        if c * c == num2 * num2 + num3 * num3:
            print("Your triangle is a pythagorean triangle")
        else:
            print("Your triangle isn't a pythagorean triangle")


    elif num2 > num1 and num2 > num3:                             # c - hypotenuse

        c = num2

        if c * c == num1 * num1 + num3 * num3:
            print("Your triangle is a pythagorean triangle")
        else:
            print("Your triangle isn't a pythagorean triangle")


    elif num3 > num1 and num3 > num2:

        c = num3

        if c * c == num2 * num2 + num1 * num1:
            print("Your triangle is a pythagorean triangle")
        else:
            print("Your triangle isn't a  pythagorean triangle")

    elif num1 == num2 and num2 == num3 and num1 == num3:
        print("There's no such thing as a pythagorean triangle with all sides the same, try again")

        again = str(input("Do you want to continue? [Y/n]n"))

        if again == "Y" or again == "y":
            pass
        else:
            break

num1, num2, num3 = sorted( [num1, num2, num3] )

# here the num1 < num2 < num3 so you may use a single check
if num1 * num1 + num2 * num2 == num 3 * num3 : # etc...