def show():
    print "balance currently:", balance

def deposit(amount):
    global balance
    print "deposit:", amount
    balance = balance + amount

def withdraw(amount):
    global balance
    print "withdraw:", amount
    balance = balance - amount

balance = 0

deposit(3)
show()
deposit(5)
show()
withdraw(2)
show()


============
>>> 
deposit: 3
balance currently: 3
deposit: 5
balance currently: 8
withdraw: 2
balance currently: 6
>>>