Lists, Strings, and Random

Strings to Lists and Back

There are two useful string methods that are often used with lists:

• split turns a string into a list based on a separator string
• join turns a list into a string based on the string it's called on
• what would the following code output? →

comics = "ranma,maison ikkoku,scott pilgrim"
awesome_comics_list = comics.split(",")
print(awesome_comics_list)
print(" and ".join(awesome_comics_list))

['ranma', 'maison ikkoku', 'scott pilgrim']
ranma and maison ikkoku and scott pilgrim

Split and Join

If I have the following list, how do I put together each element with an exclamation point and space between each element? How do I turn the resulting string back to a list? →

hello = ["Bill", "Phil", "Gil", "Jill"]

names = "! ".join(hello)
print(names)
print(names.split("! "))

Random - Choice, Shuffle

The random module offers some methods that can be used on lists:

• choice(my_list): retrieves a random item from the supplied list
• shuffle(my_list): randomly changes the order of the elements in the list passed in (in place)

Let's try using a couple of these methods →

import random
numbers = [1, 2, 3, 4, 5, 6, 7]
print(random.choice(numbers))
random.shuffle(numbers)
print(numbers)

One Hand of Blackjack

• try implementing a single hand of blackjack
  • sum of cards is closest or equal to 21 without going over
  • dealt a hand of two cards, can either keep drawing or stop
• use a commandline interface:
  • 'h' for hit / draw more cards
  • 's' for stay / stop drawing cards
• create a computer opponent that determines whether or not to keep getting cards

Break Down the Problem

• what data do we want to store, and how do we represent it?
• shuffling and distributing cards
• calculating a blackjack hand
• dealing with user input
• playing as the computer
• determining who won

Representing Data

What data do we want to store, and how do we represent it?

Shuffling and Distributing Cards

Write a short program that: →

• creates a deck of cards as a list of strings: 2-9, A, K, Q, J (4 x for hearts, clubs, spades, clovers)
• mix up the deck
• distribute two cards to both the player and the computer

# create deck and deal
deck = ['2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A'] * 4
random.shuffle(deck)
player_hand = []
computer_hand = []
for i in range(2):
	player_hand.append(deck.pop())
	computer_hand.append(deck.pop())

Calculating a Blackjack Hand

Implement a function that takes a list of strings representing cards. It should calculate the sum of the cards

• represent cards as a list of strings: 1-9, A, K, Q, J
• face cards count as 10
• aces count as either 1 or 11… choose the value that brings the sum closest to 21
• implement a function that takes a list of strings
• it should return an integer that represents the total of the cards
• write pseudocode to determine how your function would choose 1 or 11
• write assertions (try multiple aces)

Some Assertions

We can check out all possible combinations of 1's and 11's to see which is the closest combination to 21.

assert 21 == current_total(['A', '9', 'A']), "two aces, one 11 and one 1"
assert 12 == current_total(['A', 'A', '10']), "two aces, both 1"
assert 21 == current_total(['A', 'A', 'A', '8']), "three aces, one 11 and two 1"
assert 12 == current_total(['A', 'A', 'A', '9']), "three aces, three 1"

Let's Think of Some Algorithms

How about this one? →

Calculating a Blackjack Hand

def current_total(hand):
	""" Sums the cards in hand.  Aces count as 1 or 11.  Will optimize for 
	highest total without going over 21. """
	total, aces = 0, 0
	for card in hand:
		if card.isdigit():
			total += int(card)
		elif card in 'JQK':
			total += 10
		elif card == 'A':
			aces += 1
			total += 11
	for i in range(aces):
		if total > 21:
			total -= 10
	return total

assert 21 == current_total(['A', '9', 'A']), "two aces, one 11 and one 1"
assert 12 == current_total(['A', 'A', '10']), "two aces, both 1"
assert 21 == current_total(['A', 'A', 'A', '8']), "three aces, one 11 and two 1"
assert 12 == current_total(['A', 'A', 'A', '9']), "three aces, three 1"

And The Rest

Maybe for homework?

• dealing with user input
• let the computer move
• who won?