[Edu-sig] Programming for the fun of it

[Kirby Urner]

Jeff Elkner wrote:
>  #!/usr/bin/python
>  import time
>  import random
>
>  notes = ['C', 'D', 'E', 'F', 'G']
>
>  while 1:
>    print "Now play " + notes[random.randint(0, len(notes) - 1)] + " . .
>. ."
>    time.sleep(2)

Just wanted to remind you about the random.choice() method, which
picks from a list directly, allowing you to bypass the indexing
syntax e.g.

  >>> import time,random
  >>> def play()
          notes = ['C', 'D', 'E', 'F', 'G']
          while 1:
             print "Now play " + random.choice(notes)+ " . . . . "
             time.sleep(2)

  >>> play()
  Now play C . .
  Now play G . .
  Now play E . .

etc.

On the random.randint() front, I've been playing around with 
cryptography, implemented a slow (put pretty) Blowfish, and
now I'm looking at RSA.  That starts with the requirement for
2 100-digit prime numbers (shall we say).  So what's a quick 
and dirty way to get some random 100-digit primes (allowing 
pseudorandom digit-picking for now)? 

Step one is to get any 100-digit number at all.  If it's even
then add 1, or if odd and easily divisible by a low prime, then 
add 2, and keep going until your prime tests (whatever they 
might be) certify the primehood of your candidate.

So let's do step one this way:

>>> def mkrandint(digits):
	bignum = ""
	for i in range(digits):
	   bignum = bignum + str(random.randint(0,9))
	return long(bignum)

>>> mkrandint(100)
7963087367299610171220441460319216044629224943047806172386921
203875082185538604305205721605709979869L

That's a big number all right.  Dunno if it's prime (probably
not) -- I don't have the tests for that written.  A Fermat test 
seems impractical.  Has anyone done Miller-Rabin in pure Python, 
for pedagogic purposes?  Still looking into it.  Yes, I know, 
I know, I need to join the Python cryptography SIG.

Kirby