Finds sf, only between 1/4 and 4

03_find_scale_factor.py

# Functions go here
def num_check(question):
    error = "Please enter a number that is more than zero"

    valid = False
    while not valid:
        try:
            response = float(input(question))

            if response <= 0:
                print(error)
            else:
                return response

        except ValueError:
            print(error)


# Main Routine goes here
sf_ok = "no"
while sf_ok == "no":

    serving_size = num_check("What is the recipe serving size? ")
    desired_size = num_check("How many servings are needed? ")

    scale_factor = desired_size / serving_size

    if scale_factor < 0.25:
        sf_ok = input("Warning: this scale factor is very small and you might struggle to accurately weigh the ingredients.  Please consider using a larger scale factor and freezing the left-overs. \nDo you want to keep going (type 'no' to change your desired serving size) ").lower()
    elif scale_factor > 4:
        sf_ok = input("Warning: this scale factor is quite large - you might have issues with mixing bowl volumes and oven space.  Please consider using a smaller scale factor and making more than one batch. \nDo you want to keep going (type 'no' to change your desired serving size) ").lower()
    else:
        sf_ok = "Yes"


print("Scale factor: {}".format(scale_factor))