analyze use of the shift key for typing passwords

gistfile1.py

import random

alpha_lower = 'abcdefghijklmnopqrstuvwxyz'
alpha_upper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
numeric = '0123456789'
punct = '''`-=[]\;',./'''
shift_punct = '!@#$%^&*()~_+{}|:"<>?'

shift_chars = set(c for c in alpha_upper + shift_punct)

def count_shifts(text):
    """count the number of times the shift key must be pressed to type a given
    string of text. assume shift key is held down between consecutive characters
    requiring shift"""
    shifted = False
    count = 0
    for c in text:
        needs_shift = (c in shift_chars)
        if needs_shift and not shifted:
            count += 1
        shifted = needs_shift
    return count

def random_text(alphabet=alpha_lower + numeric + alpha_upper, length=8):
    """generate random text"""
    return ''.join(random.choice(alphabet) for i in range(length))

def trial(alphabet, length, n):
    """perform trail runs to determine the average number of required
    shift-key pressings per character"""
    return sum(count_shifts(random_text(alphabet, length)) for i in range(n)) / float(length * n)