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tournament.py
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tournament.py
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#!/usr/bin/env python
#
# tournament.py -- implementation of a Swiss-system tournament
# This implementation influenced by the directions provided
# by DCI http://www.wizards.com/dci/downloads/swiss_pairings.pdf
import psycopg2
def connect():
"""Connect to the PostgreSQL database. Returns a database connection."""
return psycopg2.connect("dbname=tournament")
def deleteMatches():
"""Remove all the match records from the database."""
conn = connect()
c = conn.cursor()
c.execute('''DELETE FROM match_outcomes;''')
c.execute('''DELETE FROM matches;''')
conn.commit()
conn.close()
def deletePlayers():
"""Remove all the player records from the database."""
conn = connect()
c = conn.cursor()
c.execute('''DELETE FROM players;''')
conn.commit()
conn.close()
def countPlayers():
"""Returns the number of players currently registered."""
conn = connect()
c = conn.cursor()
c.execute('''SELECT count(*)
FROM players;''')
number_of_players = c.fetchone()[0]
conn.close()
return number_of_players
def registerPlayer(name):
"""Adds a player to the tournament database.
Args:
name: the player's full name (need not be unique).
"""
conn = connect()
c = conn.cursor()
c.execute('''INSERT INTO players (name, bye)
VALUES (%s, FALSE);''', (name,))
conn.commit()
conn.close()
def playerStandings():
"""Returns a list of the players and their win records, sorted by points
determined by the formula 3*wins + 3*byes + draws. This scoring scheme
is taken from http://www.wizards.com/dci/downloads/swiss_pairings.pdf
Returns:
A list of tuples, each of which contains (id, name, wins, matches):
id: the player's unique id (assigned by the database)
name: the player's full name (as registered)
wins: the number of matches the player has won
matches: the number of matches the player has played
"""
conn = connect()
c = conn.cursor()
c.execute('''SELECT id,
name,
wins,
matches
FROM ranked_players;''')
standings = c.fetchall()
conn.close()
return standings
def reportMatch(winner, loser = None, draw = False):
"""Records the outcome of a single match between two players (or one player for byes).
Args:
winner: the id number of the player who won or received a bye
loser: the id number of the player who lost. If None, then winner is a bye.
draw = boolean of whether match resulted in draw.
"""
if loser == None and draw == True:
raise ValueError("If loser is not specified, the match cannot be a draw (must be a bye).")
conn = connect()
c = conn.cursor()
#Add a new match id m_id and retrieve it.
c.execute('''INSERT INTO matches DEFAULT VALUES;''')
c.execute('''SELECT max(id) FROM matches;''')
m_id = c.fetchone()
if not loser:
#Then count player as a bye
c.execute('''INSERT INTO match_outcomes
(match_id,
player,
player_outcome)
VALUES (%s, %s, 'B');''', (m_id, winner))
elif draw:
#Assign each player a draw
c.execute('''INSERT INTO match_outcomes
(match_id,
player,
player_outcome)
VALUES (%s, %s, 'D');''', (m_id, winner))
c.execute('''INSERT INTO match_outcomes
(match_id,
player,
player_outcome)
VALUES (%s, %s, 'D');''', (m_id, loser))
else:
#Assign winner and loser matches accordingly
c.execute('''INSERT INTO match_outcomes
(match_id,
player,
player_outcome)
VALUES (%s, %s, 'W');''', (m_id, winner))
c.execute('''INSERT INTO match_outcomes
(match_id,
player,
player_outcome)
VALUES (%s, %s, 'L');''', (m_id, loser))
conn.commit()
conn.close()
def swissPairings():
"""Returns a list of pairs of players for the next round of a match.
Assuming that there are an even number of players registered, each player
appears exactly once in the pairings. Each player is paired with another
player with an equal or nearly-equal score (3 * #wins + 3 * #byes + #draws).
That is, a player is matched to the player adjacent in the standings in the
ranked_players view.
If there are an odd number of players, a bye is assigned to a player that has
not received one yet and that player is not returned in the list of pairs.
Returns:
A list of tuples, each of which contains (id1, name1, id2, name2)
id1: the first player's unique id
name1: the first player's name
id2: the second player's unique id
name2: the second player's name
"""
conn = connect()
c = conn.cursor()
#Assign a bye if there are odd # players
odd_num_players = countPlayers() % 2
bye_player = -1
if odd_num_players:
c.execute('''SELECT id
FROM players
WHERE bye = FALSE;''')
bye_player = c.fetchone()[0]
reportMatch(winner = bye_player)
c.execute('''UPDATE players
SET bye = TRUE
WHERE id = %s;''', (bye_player,))
conn.commit()
#If all of the players have a bye, then reassign
#everyone's bye to 0 to restart the process.
c.execute('''SELECT *
FROM players
WHERE bye = FALSE;''')
if not c.fetchall():
c.execute('''UPDATE players
SET bye = FALSE;''')
#Select pairs from the ranked_players view with the bye player removed.
c.execute('''WITH ranked_removing_bye AS
(SELECT * FROM ranked_players WHERE ranked_players.id != %s)
SELECT t1.id,
t1.name,
t2.id,
t2.name
FROM ranked_removing_bye AS t1
JOIN ranked_removing_bye AS t2 ON t1.player_rank + 1 = t2.player_rank
WHERE mod(t1.player_rank, 2) = 1
AND mod(t2.player_rank, 2) = 0;''', (bye_player, ))
pairs = c.fetchall()
conn.close()
return pairs