"""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 Cookie(Pmf):
"""A map from string bowl ID to probablity."""
def __init__(self, hypos):
"""Initialize self.
hypos: sequence of string bowl IDs
"""
Pmf.__init__(self)
for hypo in hypos:
self.Set(hypo, 1)
self.Normalize()
def Update(self, data):
"""Updates the PMF with new data.
data: string cookie type
"""
for hypo in self.Values():
like = self.Likelihood(data, hypo)
self.Mult(hypo, like)
self.Normalize()
mixes = {
'Bowl 1':dict(vanilla=0.75, chocolate=0.25),
'Bowl 2':dict(vanilla=0.5, chocolate=0.5),
}
def Likelihood(self, data, hypo):
"""The likelihood of the data under the hypothesis.
data: string cookie type
hypo: string bowl ID
"""
mix = self.mixes[hypo]
like = mix[data]
return like
def main():
hypos = ['Bowl 1', 'Bowl 2']
pmf = Cookie(hypos)
pmf.Update('vanilla')
for hypo, prob in pmf.Items():
print hypo, prob
if __name__ == '__main__':
main()
