Lecture 13
Non-Local Assignment & Persistent Local State

def make_withdraw(balance):
  def withdraw(amount):
    nonlocal balance
    if amount > balance:
      return "Insufficient funds"
    balance = balance - amount
    return balance
  return withdraw        

Reference Transparency

def f(x):
  x = 4
  def g(y):
    def h(z):
      nonlocal x
      x = x + 1
      return x + y + z
    return h
  return g

>>> a = f(1)
>>> b = a(2)
>>> total = b(3) + b(4)
>>> total
22    

计算b(3)时nonlocal x = 4，所以x + 1 = 5， 计算b(4)时调用x时x为5，此时 x + 1 = 6

Lecture 14
Object-Oriented Programming
Object Construction

class Account:
  def __init__(self, account_holder):
    self.balance = 0
    self.holder = account_holder    

>>> a = Account('Zhou')
>>> a.balance
0
>>> a.holder
'Zhou'

Methods

class Account:
  interest = 0.02 # A class attribute
  def __init__(self, account_holder):
    self.balance = 0
    self.holder = account_holder 
  def deposit(self, amount):
    self.balance += amount
  return self.balance
  def withdraw(self, amount):
    if amount > self.balance:
      return "Insufficient funds"
    self.balance -= amount
    return self.balance

Lecture 15
Inheritance

class CheckingAccount(Account):
  interest = 0.01
  withdraw_fee = 1
  def withdraw(amount):
    return Account.withdraw(self, self.amount + withdraw_fee)     

Multiple Inheritance

class SavingAccount(Account):
  deposit_fee = 2
  def deposit(amount):
    return Account.deposit(self, self.amount - deposit_fee)

class BestAccount(CheckingAccount, SavingAccount):
  def __init__(self, account_holder):
    self.balance = 1
    self.holder = account_holder     

Composition

class Bank:
  def __init__(self):
    self.accounts = [] # composition
  def open_account(self, holder, amount, account_type=Account):
   account = account_type(holder)  
   account.deposit(amount)
   self.accounts.append(account)
  return account
def pay_interest(self):
   for account in self.accounts:
    account.deposit(account.balance * account.interest)

Lecture 16