# the bank uses this exception to say there's something wrong:
class BankError(Exception): pass

# Unrestricted account.
class Account:
	def __init__(s):
		s._balance=0.0
	def withdraw(s, amount):
		s._balance=s._balance-amount
	def deposit(s,amount):
		s._balance=s._balance+amount
	def balance(s):
		return s._balance

# Restricted withdrawal account.
class RestrictedAccount(Account):
	def withdraw(s, amount):
		if amount<=s._balance:
			s._balance=s._balance-amount
		else:
			raise BankError('insufficent balance')

# Abstract bank.
class Bank:
	def __init__(s):
		s.accounts={}
	def name(s):
		pass # must override this!
	def createAccount(s, name):
		pass # must override this!
	def deleteAccount(s, name):
		try:
			del s.accounts[name]
		except KeyError:
			raise BankError('unknown account')
	def deposit(s, name, amount):
		try:
			return s.accounts[name].deposit(amount)
		except KeyError:
			raise BankError('unknown account')
	def withdraw(s, name, amount):
		try:
			return s.accounts[name].withdraw(amount)
		except KeyError:
			raise BankError('unknown account')
	def balance(s, name):
		try:
			return s.accounts[name].balance()
		except KeyError:
			raise BankError('unknown account')
	def allAccounts(s):
		accs = {}
		for name in s.accounts.keys():
			accs[name] = s.accounts[name].balance()
		return accs


# Special bank: Rabobank. It has unrestricted accounts.
class Rabobank(Bank):
	def name(s):
		return 'Rabobank'
	def createAccount(s,name):
		if s.accounts.has_key(name):
			raise BankError('Account already exists')
		s.accounts[name]=Account()


# Special bank: VSB. It has restricted accounts.
class VSB(Bank):
	def name(s):
		return 'VSB bank'
	def createAccount(s,name):
		if s.accounts.has_key(name):
			raise BankError('Account already exists')
		s.accounts[name]=RestrictedAccount()