birthday.py

#!/usr/bin/env python

import math, random, sys, json
from decimal import Decimal as dml

print ("This will simulate the 'Birthday Problem' by generating XX random")
print ("numbers between 1 and 365 (inclusively).\n")

# number of people per trial
people = int(sys.argv[1])
# number of trails
trials = int(sys.argv[2])
n_trials = trials

matches = 0
nomatches = 0
total_trials = trials

def findmatches( numbers ):
    s = set()
    ans = False
    for number in numbers:
        if numbers.count(number) > 1:
            s.add(number)
            ans = True
    return ans, s

while trials > 0:
    trials -= 1
    
    # Seed random with the current time, creates more "randomness" on each iteration
    random.seed()
    
    #generate a list of "people" length, where each element is a random number between from 1 (inclusive) to 366 (non-inclusive)
    numbers = [random.randrange(1,366) for i in range(people)]

    #print "Here is the list of numbers: "
    #for number in numbers:
        #print number
        
    a,b = findmatches(numbers)
    
    if a == True:
        matches += 1
    
    #print "Trial:",total_trials - trials

result = dml(matches) / dml(total_trials) * 100
expected =  (1 - dml(math.factorial(365)) / ( 365**people * math.factorial(365-people)))*100
if result != 0:
    pe = abs( (expected - dml(result) ) / dml(result)) * 100
else:
    print ("\nPlease enter more trials, to prevent a division by zero!\n")
    sys.exit()

output_json = json.dumps({'total_trials':n_trials, 'num_people': people, 'num_successful_trials':matches, 'percent_successful_trials': str(round(result,4)), 'expected_successful_trials':str(round(expected,4)), 'percent_error':str(round(pe,4))})
print(output_json)