[Tutor] Giving a name to a function and calling it, rather than calling the function directly

[Alex Hall]

On 9/4/10, lists <lists at justuber.com> wrote:
> Hi folks,
>
> I'm new to Python, I'm working my way through some intro books, and I
> have a question that I wonder if someone could help me with please?
>
> This is my attempt at solving an exercise where the program is
> supposed to flip a coin 100 times and then tell you the number of
> heads and tails.
>
> ATTEMPT 1 returns:
>
> The coin landed on tails 100 times
>
> The coin landed on heads 0 times
>
> ATTEMPT 2 returns:
>
> The coin landed on tails 75 times
>
> The coin landed on heads 25 times
>
> I expected to see the result in attempt 2. I don't fully understand
> why the results are different however. Is it because Python only runs
> the randint function once when I call it by the name I assigned to it
> in attempt 1, but it runs the function fully on each iteration of the
> loop in attempt 2? Why are these two things different?
Exactly. Essentially when you say
x=random.randint(1,2)
you are putting the value returned by randint into x, and this happens
only once. Had you moved that assignment into the while loop it would
keep replacing x, or toss in your case, with a random integer, but
because you just call it once it is only assigned once. Python, or any
language, would have no way of knowing that you want to reassign toss
each time. Loops are used to repeat actions, but you left the
assignment of your random int outside of the loop in attempt1 and so
there is no way for Python to know that you actually want toss updated
100 times. I hope I explained this okay.
>
> Thanks in advance,
>
> Chris
> ------------------------------------------------------------------
> ATTEMPT 1
> ------------------------------------------------------------------
> import random
>
> heads = 0
> tails = 0
> tossNo = 0
> toss = random.randint(1,2)
>
> while tossNo <= 99:
>     if toss == 1:
>         heads += 1
>         tossNo += 1
>     elif toss == 2:
>          tails += 1
>          tossNo += 1
>
> print "The coin landed on tails " + str(tails) + " times \n"
> print "The coin landed on heads " + str(heads) + " times \n"
>
> ------------------------------------------------------------------
> ATTEMPT 2
> ------------------------------------------------------------------
> import random
>
> heads = 0
> tails = 0
> tossNo = 0
>
> while tossNo <= 99:
>     if random.randint(1,2) == 1:
>         heads += 1
>         tossNo += 1
>     elif random.randint(1,2) == 2:
>          tails += 1
>          tossNo += 1
>
> print "The coin landed on tails " + str(tails) + " times \n"
> print "The coin landed on heads " + str(heads) + " times \n"
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-- 
Have a great day,
Alex (msg sent from GMail website)
mehgcap at gmail.com; http://www.facebook.com/mehgcap