A Simple ATM Machine

"""
a simple ATM machine.
"""

import pickle
from sys import exit

try:
    accounts = pickle.load(open('accounts.p', 'rb'))
except IOError:
    accounts = {}


def UserFound(user):
    if user in accounts:
        return True
    else:
        return False

def CreateAccount(user):
    accounts[user] = 0

def Withdraw(user, balance):
    try:
        accounts[user] -= balance
    except TypeError:
        print '{} is not a possible value.'.format(balance)

def Deposit(user, balance):
    try:
        accounts[user] += balance
    except TypeError:
        print '{} is not a possible value.'.format(balance)

def GetBalance():
    print 'Your balance is: {}'.format(accounts[user])


user = raw_input('What is your full name?\n')


def MainMenu():
    global user
    print "Welcome {}! What do you want to do?\n1 - Create Account".format(user)
    print "2 - Withdraw Money\n3 - Deposit Money\n4 - See Balance\n5 - Exit\n"
    choice = int(raw_input())
    if choice == 1:
        user = raw_input('What is your full name?\n')
        CreateAccount(user)
        MainMenu()
    elif choice == 2:
        if UserFound(user):
            amount = raw_input('Enter the withdraw amount.')
            Withdraw(user, amount)
            GetBalance()
            MainMenu()
        else:
            print 'User not found.'
            MainMenu()
    elif choice == 3:
        if UserFound(user):
            amount = raw_input('Enter the deposit amount.')
            Deposit(user, amount)
            GetBalance()
            MainMenu()
        else:
            print 'User not found.'
            MainMenu()
    elif choice == 4:
        GetBalance()
        MainMenu()
    elif choice == 5:
        pickle.dump(accounts, open('accounts.p','wb'))
        exit()

MainMenu()