BankTeller Project for Python 3path in data science

Below is the code for my first project in the data science path. I would love any feedback and any help in regards to updating the main variables (checking_balance and savings_balance). The app seems to work pretty well however while all the functions work independently, the variable values do not stay updated while using the app.

Thanks for any feedback!

Welcome to my Bank Teller / ATM Application
AS you read thru the code below you'll find 6 total functions The first four represent the functionallity of the BankTeller/ATM Then there is an exit function Finally it is all wrapped together in a startApp function which fires the program up

## First function to check balance
## Run this function to check balances of both accounts
​
def check_balance(account_type,checking_balance,savings_balance): 
    if account_type == 'checking':
            print("You are interested in checking")
            balance = checking_balance
        
    elif account_type == 'savings':
        print("you are interested in savings")
        balance = savings_balance
        
    else:
        return acc_error
    
    balance_statement = "Your " + account_type + " balance is " + str(balance)
    print(balance_statement)
    return checking_balance,savings_balance
    
## Deposit function, takes 4 parameters specifying the account and amount
## last two parameters pass thru balances and return balance
## this function will be wrapped in a start function
​
def deposit(account_type,deposit_amount,checking_balance,savings_balance):
    deposit_status = ""
    if deposit_amount > 0:
        if account_type == 'checking':
            checking_balance += deposit_amount
            deposit_status = ("Succesfull")                   
        elif account_type == 'savings':
            savings_balance += deposit_amount
            deposit_status = ("Succesfull")           
        else:
            deposit_status = "Unsucessful!"
            print(deposit_status + ' try again ')
            startApp()                      
    else:
        deposit_status = "Unsuccesful, please enter a value greater than 0"
        
    deposit_statement = "Deposit of " + str(deposit_amount) + " to your " + account_type + " account was " + deposit_status    
    print(deposit_statement)
    return checking_balance, savings_balance
    
## withdrawl function with 4 parameters
## this function will be wrapped and called in a start function
​
def withdrawl(account_type,withdrawl_amount,checking_balance,savings_balance):
    withdrawl_status = ''
    if withdrawl_amount >= 0:
        if account_type == 'checking':
            if withdrawl_amount <= checking_balance:
                withdrawl_status = "Successful!"
                checking_balance -= withdrawl_amount
            else:
                print("Insufficent Funds!")
        
        elif account_type == "savings":
            if withdrawl_amount <= savings_balance:
                withdrawl_status = "Successful!"
                savings_balance -= withdrawl_amount
            else:
                print("Insufficent Funds!")
    else:
        withdrawl_status = "Unsuccessfull"
        return withdrawl_status
    
    withdrawl_statement = "your withdrawl from your " + account_type + " account of " + str(withdrawl_amount) + " dollars is successfull!"
    
    if withdrawl_status == "Successful!":
        print(withdrawl_statement)
    else:
        print("fuk you")
    
    return checking_balance,savings_balance
​
​
##Transfer function to move funds from one account to another
## This function will be called in the start function
​
def transfer(account_from,account_to,transfer_amount,checking_balance,savings_balance):
    a = account_from
    b = account_to
    if a == 'checking':
        if transfer_amount > checking_balance:
            print("Insufficent Funds")
            return 0
        else:
            print('------ Processing Transfer ----------')
            checking_balance -= transfer_amount
            savings_balance += transfer_amount        
            print("Transfer Successful!")
            return checking_balance,savings_balance
        
    elif a == 'savings':
        if transfer_amount > savings_balance:
            print('Insufficent Funds')
            return 0
        else:
            print('------ Processing Transfer ----------')
            savings_balance -= transfer_amount
            checking_balance += transfer_amount
            print("Transfer Successful!")
            return checking_balance,savings_balance
    
    else:
        print('enter correct acount information')
​
## Exit function to shut the program down
def exitApp():
    exit()
​
## Starting Function to run the program
## Calling this function gives the user access to all other functionallity 
​
def startApp():
    checking_balance = 0
    savings_balance = 0
    
    print('------ Welcome to your new Banking Application, What would you like to do? ' )
    
    print("""
            [1] -- Check Balance
            [2] -- Make Deposit
            [3] -- Make Withdrawl
            [4] -- Initiate Transfer
            [5] -- Exit Program
    
            """)
    userInput = input("Enter The Corresponding Number ")
    
    if userInput == '1':
        
        account_type = input('What account? ' )
        checking_balance = checking_balance
        savings_balance = savings_balance
        
        check_balance(account_type,checking_balance,savings_balance)
    
    elif userInput == '2':       
        account_type = input('What account? ' )
        deposit_amount = int(input('How Much Would You Like to Deposit? ' ))
        checking_balance = checking_balance
        savings_balance = savings_balance
        
        deposit(account_type,deposit_amount,checking_balance,savings_balance)
        
    elif userInput == '3':
        account_type = input('What account? ' )
        withdrawl_amount = int(input('How Much Would You Like to Withdraw? ' ))
        checking_balance = checking_balance
        savings_balance = savings_balance
        
        withdrawl(account_type,withdrawl_amount,checking_balance,savings_balance)
        
    elif userInput == '4':
        account_from = input('Which account would you like to transfer from? ' )
        account_to = input('Which account would you like to transfer to? ' )
        transfer_amount = int(input('How much would you like to transfer? ' ))
        checking_balance = checking_balance
        savings_balance - savings_balance
        
        transfer(account_from,account_to,transfer_amount,checking_balance,savings_balance)
    
    elif userInput == '5':
        exitApp()
               
    else:
        print("Choose a number 1-5")
    
    userInput = input("Would you like to perform another task? yes or no? " )
    if userInput == 'yes':
        startApp()
    elif userInput == 'no':
        exitApp()
    
## call the start app when program opens      
startApp()

here:

    if userInput == 'yes':
        startApp()
    elif userInput == 'no':
        exitApp()
 

calling startApp again, means these lines:

    checking_balance = 0
    savings_balance = 0

get executed again, overwriting any deposits/withdraws you have done by setting these variables to zero