"""This file contains code for use with "Think Bayes",
by Allen B. Downey, available from greenteapress.com
Copyright 2012 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
"""
from thinkbayes import Pmf
class Monty(Pmf):
"""Map from string location of car to probability"""
def __init__(self, hypos):
"""Initialize the distribution.
hypos: sequence of hypotheses
"""
Pmf.__init__(self)
for hypo in hypos:
self.Set(hypo, 1)
self.Normalize()
def Update(self, data):
"""Updates each hypothesis based on the data.
data: any representation of the data
"""
for hypo in self.Values():
like = self.Likelihood(data, hypo)
self.Mult(hypo, like)
self.Normalize()
def Likelihood(self, data, hypo):
"""Compute the likelihood of the data under the hypothesis.
hypo: string name of the door where the prize is
data: string name of the door Monty opened
"""
if hypo == data:
return 0
elif hypo == 'A':
return 0.5
else:
return 1
def main():
hypos = 'ABC'
pmf = Monty(hypos)
data = 'B'
pmf.Update(data)
for hypo, prob in sorted(pmf.Items()):
print hypo, prob
if __name__ == '__main__':
main()
