scrabble-prob.py

#!/usr/bin/env python

data = """a 9
b 2
c 2
d 4
e 12
f 2
g 3
h 2
i 9
j 1
k 1
l 1
m 2
n 6
o 8
p 2
q 1
r 6
s 4
t 6
u 4
v 2
w 2
x 1
y 2
z 1

""" # final blank line needed to denote EOF

"""
    data = line* . eof
    line = letter . space . count . newline
    count = digit+
     eof = newline
"""

class string_reader(object):
    def __init__(self, st):
        self.ix, self.st = 0, st
    def getch(self):
        self.ix += 1
        return self.st[self.ix-1]

def is_letter(ch): return 'a' <= ch <= 'z'
def is_digit(ch): return '0' <= ch <= '9'

def load_pairs(data=data):
    # do it the hard way
    sr = string_reader(data)
    counts = []
    ch = sr.getch()
    while ch != '\n':
        assert is_letter(ch), `ch`
        letter = ch
        ch = sr.getch()
        assert ch == ' ', `ch`
        count = 0
        ch = sr.getch()
        while is_digit(ch):
            count = 10 * count + (ord(ch) - ord('0'))
            ch = sr.getch()
        assert ch == '\n', `ch`
        counts.append((letter, count))
        ch = sr.getch()
    return counts

def load_pairs_adhoc(data=data): # not used
    return [
        (ch,int(n)) for (ch,n) in [
            s.strip().split() for s in data.strip().split('\n')]]

def prob_distribution(counts):
    total = 1.0 * sum(i for (_,i) in counts)
    return set((ch,i/total) for (ch,i) in counts)

"""
A set of disjoint outcomes is an 'event'. The probability of an event
is the sum of probabilities of its outcomes.

Compute the probability of drawing a vowel from the intital set of
scrabble tiles.
"""
pb = prob_distribution(load_pairs())
VOWELS = set(ch for ch in "aeiou")
print sum(p for (l,p) in pb if l in VOWELS)