Python COM and distribution issues

[hungjunglu at yahoo.com]

--- In python-list at y..., Tim Roberts <timr at p...> wrote:
> You are incorrect.  Do the math.  If you had been generating a 
billion
> GUIDs per second, for every second since the big bang, you would 
still have
> generated only one billionth of the possible GUIDs.  2^128 is 
unfathomably
> large.

There is a famous birthday problem for probability as taught in high 
schools: "What is the typical size of a class for two persons to have 
the same birthday?" Most people would say that since there are 365 
days, they'd guess somewhere around half that number, that is, for a 
class of around 180 students.

The actual number is more like the square root of 365, that is, for a 
group of 20 people or so (order of magnitude), you'd already have a 
pretty good chance of finding two people with the same birthday. 

For p students, the probability of finding NO students with the same 
birthday is about 

   prob. for zero collision = exp[p(p-1)/(2N)] (where N=365)

For p=20 students, that is 0.6

For p=180 students, that is exp[-44] = 10^(-20) = 
0.00000000000000000001 (order-of-magnitude-wise speaking)

Or conversely, you have 40% chance of finding 2 people with the same 
birthday in class size of 20 students. And you have better than 
0.99999999999999999999 probability of finding students with same 
birthday in a class of size 180. Matter of fact, you probably find 
about 10 people with birthday collisions, maybe more.

Now, that's well-known and I am sure you have done the math yourself, 
you just forgot how to do the math, now.

2^128 is about 3.4x10^39, square root of that is 10^19 or so. There 
are 10^7 seconds in a year (order of magnitude), age of universe is 
about 10^10 years. If you generate a billion (10^9) GUIDs per second, 
I'd say you have about (7+10+9-19) = 7 orders of power of 10, that 
is, tens of millions of GUID collisions.

Suddenly 2^128 does not seem to be "unfathomably large" anymore. 
Right?

I did the math, years ago. Don't tell people to do the math when you 
yourself cannot do the math. :)

regards,

Hung Jung