On 22/06/13 00:32, Wolfgang Maier wrote:
Arijit Ukil <arijit.ukil <at> tcs.com> writes:
I have following random number generation
function
def
rand_int ():
rand_num = int(math.ceil
(random.random()*1000))
return
rand_num
I like to make the value of rand_num
(return of rand_int) static/ unchanged after first call even if it is called
multiple times. If x= rand_int () returns 45 at the first call, x
should retain 45 even in multiple calls.
Sifting through the random module documentation a bit:
def rand_int(update=False):
if update:
dummy = random.random()
oldstate=random.getstate()
rand_num = random.randint(0,1000)
random.setstate(oldstate)
return rand_num
This will return a constant number when called with a False value for update
(the default), but will switch to returning a new number when called
with a True value once.
You really don't want to do this! By doing this, every time you call your
rand_int() function, you will reset the application-wide pseudo-random number
generator, possibly making a mess of other parts of your application and the
standard library.
You also throw away a random value, which probably won't make a difference for
the default Python PRNG, but may be bad if you're using a lousy PRNG.
There is a much simpler ways of doing this (see below), but if you must use
getstate and setstate, then you should create your own personal random number
generator rather than use the system-wide default PRNG.
myrandom = random.Random()
def rand_int(update=False):
if update:
dummy = myrandom.random()
oldstate = myrandom.getstate()
rand_num = myrandom.randint(0, 1000)
myrandom.setstate(oldstate)
return rand_num
This doesn't look like much, but it's actually an awful lot of work just to
return a fixed, constant number! The PRNG used by Python is *very good*, which
means it is also computationally quite expensive. Here's a cheaper way to get
the same effect, using a mutable default argument to store the last result,
then only call the PRNG when you actually need to:
def rand_int(update=False, seed=[None]):
if update or seed[0] is None:
seed[0] = random.randint(0, 1000)
return seed[0]
--
Steven
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
