Simple blackjack implementation

blackjack.py

#!/usr/bin/env python

import sys
from random import shuffle
from pprint import pformat

def group_by(keyfn, l):
  groups = {}
  for e in l:
    key = keyfn(e)
    groups.setdefault(key, [])
    groups[key].append(e)
  return groups

### Cards ###

SUITS = { s[0]: s for s in ["spades", "hearts", "clubs", "diamonds"] }
RANKS = { 1: "ace", 11: "jack", 12: "queen", 13: "king" }
SCORES = { 1: 11, 11: 10, 12: 10, 13: 10 }
STATES = {
  "busted": "You've busted!",
  "blackjack": "You hit blackjack!",
  "twentyone": "You hit 21!",
}

def new_deck():
  ranks = range(1, 14)
  return [(suit, rank) for suit in SUITS.keys() for rank in ranks]

def shuffle_deck(deck=None, times=1):
  if deck is None:
    deck = new_deck()
  for _ in range(times):
    shuffle(deck)
  return deck

def format_card(card):
  suit, rank = card
  suit_name = str(SUITS.get(suit))
  rank_name = str(RANKS.get(rank, rank))
  return "%s of %s" % (rank_name.capitalize(), suit_name.capitalize())

def format_hand(hand, sep="\n"):
  return sep.join(format_card(card) for card in hand)

### Blackjack ###

DEALER = "_dealer_"

def deal_cards(game, per_player):
  deck = game["deck"]
  hands = game["hands"]

  for _ in range(per_player):
    for player in game["players"]:
      hands[player].append(deck.pop(0))
    game["dealer"].append(deck.pop(0))

  game.update({"deck": deck, "hands": hands})
  return game

def score_card(card):
  suit, rank = card
  return SCORES.get(rank, rank)

def is_ace(card):
  suit, rank = card
  return rank == 1

def score_hand(hand):
  aces = len([c for c in hand if is_ace(c)])
  score = sum(score_card(card) for card in hand)
  while score > 21 and aces:
    score -= 10
    aces -= 1
  return score

def new_game(players):
  game = { "deck": shuffle_deck(times=7), "players": players, "hands": {},
    "dealer": [] }

  for player in players:
    game["hands"][player] = []

  return game

def hand_type(hand):
  score = score_hand(hand)
  cards = len(hand)

  if score == 21 and cards == 2:
    return "blackjack"
  elif score == 21:
    return "twentyone"
  elif score > 21:
    return "busted"

  return "normal"

WINNING = ["twentyone", "blackjack"]
LOSING = ["busted"]
COMPLETED = WINNING + LOSING

def normalize_hand(hand):
  scoring = {"blackjack": 100, "twentyone": 50, "busted": 0}
  return scoring.get(hand_type(hand), score_hand(hand))

def compare_hands(hand1, hand2):
  return cmp(normalize_hand(hand1), normalize_hand(hand2))

def determine_winners(game):
  dealer, players = game["dealer"], game["hands"].items()
  comp = lambda p: compare_hands(p[1], dealer)

  stats = group_by(comp, players)
  winners = stats.get(1, [])
  losers = stats.get(-1, [])
  pushes = stats.get(0, [])

  if hand_type(dealer) == "busted":
    losers += pushes
    pushes = []

  return (winners, losers, pushes)

### UI ###

def get_input(prompt, options=None):
  while True:
    val = raw_input(prompt)
    if options is None or val in options:
      return val

def print_menu(player):
  print "It's %s's turn" % player
  print "Press 'h' to hit"
  print "Press 's' to stay"
  print "Press 'q' to quit"

def print_hand(player, hand):
  print "\n%s's hand:" % player
  print format_hand(hand)

def player_turn(player, game):
  deck, hand = game["deck"], game["hands"][player]
  print_menu(player)
  print_hand(player, hand)

  while True:
    print "\nScore: %d" % score_hand(hand)

    htype = hand_type(hand)
    if htype in COMPLETED:
      print STATES.get(htype)
      break

    move = get_input("> ", ["h", "s", "q"])

    if move == "h":
      card = deck.pop(0)
      hand.append(card)
      print "Hit: %s" % format_card(card)
    elif move == "s":
      print "Staying"
      break
    elif move == "q":
      print "Goodbye!"
      sys.exit()

  print
  return htype

def dealer_turn(game):
  deck, hand = game["deck"], game["dealer"]

  print "It's the dealers turn"
  print "\nDealer's hand:"
  print format_hand(hand)

  while score_hand(hand) < 17:
    card = deck.pop(0)
    hand.append(card)
    print "Dealer hits: %s" % format_card(card)

  score = score_hand(hand)
  print "\nScore: %d" % score
  return score

def print_scores(game):
  print "\nScore\n"

  print "Dealer has:"
  print format_hand(game["dealer"])
  print "with a score of %d\n" % score_hand(game["dealer"])
  print

  winners, losers, pushes = determine_winners(game)

  print "Winners: "
  for winner in winners:
    name, hand = winner
    print " %s - %d" % (name, score_hand(hand))
  print

  print "Losers: "
  for loser in losers:
    name, hand = loser
    print " %s - %d" % (name, score_hand(hand))
  print

  print "Pushes: "
  for push in pushes:
    name, hand = push
    print " %s - %d" % (name, score_hand(hand))
  print

def main():
  game = new_game([chr(n) for n in range(65, 75)])
  deal_cards(game, 2)

  for player in game["players"]:
    player_turn(player, game)
  dealer_turn(game)

  print_scores(game)

if __name__ == "__main__":
  main()