Python: "Name is not defined" error

Question

So I was doing a tuition program assignment for homework the other day. This is my program. I hope it's self explanatory. (This is Python, by the way.)

def print_intro():
print ("Welcome to the tuition program. This program will calculate your tuition cost.")

def get_id_num():
    grad_status = input("Is the student an undergrad or grad (U/G)? ")
    id_num = int(input("Enter the student's ID Number: "))
    while (grad_status == "U") and (id_num < 0):
        print("Sorry, that is invalid. Please try again.")
        id_num = int(input("Enter the student's ID Number: "))  
    while (grad_status == "G") and (id_num >= 0):
        print("Sorry, that is invalid. Please try again.")
        id_num = int(input("Enter the student's ID Number: "))

def get_info():
    get_id_num()
    age = int(input("Enter the student's age (numbers only): "))
    residency = input("Is the student in-state or out-of-state (I/O)? ")
    num_credits = int(input("How many hours of credit will the student take? "))
    correct = input("Is all the above information correct (Y/N)? ")
    while correct == "N":
        print("Please enter the information correctly!")
        get_info()
    else:
        get_base_tuition()

def get_base_tuition():
    if (grad_status == "U") and (num_credits <= 6) and (residency == "I"):
        initial_tuition = 2000
    if (grad_status == "U") and (7 <= num_credits <= 11) and (residency == "I"):
        initial_tuition = 3000
    if (grad_status == "U") and (num_credits >= 12) and (residency == "I"):
        initial_tuition = 3800
    if (grad_status == "U") and (num_credits <= 6) and (residency == "O"):
        initial_tuition = 2000
    if (grad_status == "U") and (7 <= num_credits <= 11) and (residency == "O"):
        initial_tuition = 3000
    if (grad_status == "U") and (num_credits >= 12) and (residency == "O"):
        initial_tuition = 9000
    if (grad_status == "G") and (num_credits <= 6) and (residency == "I"):
        initial_tuition = 2000
    if (grad_status == "G") and (7 <= num_credits <= 11) and (residency == "I"):
        initial_tuition = 2500
    if (grad_status == "G") and (num_credits >= 12) and (residency == "I"):
        initial_tuition = 4400
    if (grad_status == "G") and (num_credits <= 6) and (residency == "O"):
        initial_tuition = 2000
    if (grad_status == "G") and (7 <= num_credits <= 11) and (residency == "O"):
        initial_tuition = 3700
    if (grad_status == "G") and (num_credits >= 12) and (residency == "O"):
        initial_tuition = 4400
    print(initial_tuition)

So after I run this, the get_info() function runs fine, up until it goes to the get_base_tuition() function. I get this error:

line 28, in get_base_tuition
    if (grad_status == "U") and (num_credits <= 6) and (residency == "I"):
NameError: name 'grad_status' is not defined

Should I have been adding parameters in my functions or something? I'm stuck and really don't know what to do. I know that if I include the variables "grad_status", "num_credits", and "residency" inside of get_base_tuition() OR define the variables inside the Python Shell before running get_base_tuition(), then of course it will work. But if I put it inside another get_base_tuition() like I did now, it won't work. Is there any way to make the get_base_tuition() function run without having to put the variables inside of get_base_tuition()? Because I already put those variables inside the functions get_id_num() and get_info(). Help is appreciated, thanks.

In case you want to know about the way the base tuition is supposed to be calculated, I attached that assignment here: Assignment Page 2

Solution

You need to read about and understand the concept of scope in Python. Here's a good answer for getting the basics on scope

Specifically in your code the grad_status variable is defined in the get_id_num function. Once the program exits that function, all the variables defined in that scope are erased and won't exist in the scope of other functions. If you have a variable that is needed in multiple functions, you need to define that variable in the global scope or pass it into each function that needs it as a parameter.