Pythagoras | Python Fiddle

# Pythagoras v1
# Author: Raymond Yang
# Date: 5/08/16
# Uses pythagoras theorem to solve equations, handles unexpected values.

def yes_no(question):
    valid = False
    while not valid:
        response = input(question)
        if response.lower() == "yes" or response.lower() == "y":
            response = "yes"
            valid = True
            return response
        elif response.lower() == "no" or response.lower() == "n":
            response = "no"
            valid = True
            return response
        else:
            print("I don't understand, enter yes / no.")
            print()

def numcheck(question, low):
    error = "Please enter a number that is more than {}".format(low)
    valid = False
    while not valid:

try:
            response = float(input(question))
            if response <= low:
                print(error)
            else:
                return response

except ValueError:
            print(error)

def numcheck_high(question, high):
    error = "Please enter a number that is less than {}".format(high)
    valid = False
    while not valid:

try:
            response = float(input(question))
            if response >= high:
                print(error)
            else:
                return response

except ValueError:
            print(error)

# main routine starts here

keep_going = "yes"
while keep_going == "yes":

# gets info
    hyp_question = yes_no("Is the hypotenuse the missing side (y/n)?")

if hyp_question.lower() == "yes" or hyp_question.lower() == "y":
        first_side_length = numcheck("What is the length of the first side?", 0)
        second_side_length = numcheck("What is the length of the second side?", 0)

# does maths
        squared = first_side_length * first_side_length + second_side_length * second_side_length
        answer = squared ** 0.5
        print("The hypotenuse side is {}".format(answer))

if hyp_question.lower() == "no" or hyp_question.lower() == "n":
        hyp_side_length = numcheck("What is the length of the hypotenuse?", 0)
        second_side_length = numcheck_high("What is the length of the second side?",hyp_side_length)

# does maths
        squared = hyp_side_length * hyp_side_length - second_side_length * second_side_length
        answer = squared ** 0.5
        print("The missing side is {}".format(answer))

# Loops program
    print()
    keep_going = yes_no("Do you want to keep going (yes / no) ? ")
    print()

# code
# first_side_length = float(input("What is the length of the first side?"))
# second_side_length = float(input("What is the length of the second side?"))
# hyp_side_length = float(input("What is the length of the hypotenuse?"))

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