Time: Wed 9/20/17 3:30 pm
One data abstraction introduced to the lecture so far: Rational numbers, represented by their numerators and denominators. Define constructors and selectors in very generalized terms.
Discuss the differences among Python list (& list comprehensions, unpacking), str (& some literals), dict. Furthermore, their use cases and how they can be useful to abstract data (like how list can be used to represent a rational number behind an abstraction barrier).
Oh, and what's an abstraction barrier after all?
If with extra time, try to implement data abstraction with higher order functions only.
# Functional version: Higher order functions
def make_ticket(ticket_type, ticket_price):
""" Makes a ticket. """
def ask(something):
""" It tells you something (the something) you are asking for. """
if something == "type":
return ticket_type
if something == "price":
return ticket_price
return "Uh oh"
return ask
def ask_ticket_type(ticket):
return ticket("type")
def ask_ticket_price(ticket):
return ticket("price")# Lab version: Representing a ticket with a list
def make_ticket(ticket_type, ticket_price):
return [ticket_type, ticket_price]
def ask_ticket_type(ticket):
return ticket[0]
def ask_ticket_price(ticket):
return ticket[1]# Super version: A number is issued to represent a ticket
tickets = []
def make_ticket(ticket_type, ticket_price):
ticket = [ticket_type, ticket_price]
tickets.append(ticket)
return len(tickets) - 1
def ask_ticket_type(ticket):
return tickets[ticket][0]
def ask_ticket_price(ticket):
return tickets[ticket][1]# Hyper version: Closure
def ticketmaster():
tickets = []
def make_ticket(ticket_type, ticket_price):
ticket = [ticket_type, ticket_price]
tickets.append(ticket)
return len(tickets) - 1
def ask_ticket_type(ticket):
return tickets[ticket][0]
def ask_ticket_price(ticket):
return tickets[ticket][1]
def print_tickets():
print(tickets)
return [make_ticket, ask_ticket_type, ask_ticket_price, print_tickets]
[make_ticket, ask_ticket_type, ask_ticket_price, print_tickets] = ticketmaster()