try_catch.py

# do calculations inside he try/catch
while True:
    try:
        length=int(input("\nPlease enter the vertical length of the square (in centimetres):  ")) 
        if length<=0 or length>150:
            print("Please enter a number between 1-150.")
            continue
        p_square=length*4
        a_square=length*length
        print("\nThe perimeter of your square is {} centimetres.".format(p_square))
        print("\nThe area of your square is {}.".format (a_square))
        break
    except ValueError:
        print("Please enter integers only.")
        
# use the try/catch *only* to take the input, do calculations once you have a valid value
while True:
    try:
        length=int(input("\nPlease enter the vertical length of the square (in centimetres):  ")) 
        if length<=0 or length>150:
            print("Please enter a number between 1-150.")
            continue
        break
    except ValueError:
        print("Please enter integers only.")
        
p_square=length*4
a_square=length*length
print("\nThe perimeter of your square is {} centimetres.".format(p_square))
print("\nThe area of your square is {}.".format (a_square))