Weird MemoryError issue

[Diez B. Roggisch]

jedi200581 at yahoo.co.uk wrote:

> Hi,
> 
>   I'm new at python as I just started to learn it, but I found out
> something weird. I have wrote a little program to compute Mersenne
> number:
> 
> # Snipet on
> def is_prime n:
>   for i in range(2, n):
>     if (n % i) == 0:
>       return 0
>   else:
>       return 1
> 
> for a in range(2, 10000000):
>   if (is_prime(a) and is_prime(2**a-1))
>     print 2**a-1, " is a prime number"
> # Snipet off
> 
> This program raise MemoryError. But this one:
> 
> # Snipet on
> def is_prime n:
>   for i in range(2, n):
>     if (n % i) == 0:
>       return 0
>   return 1 # the change is here
> 
> for a in range(2, 10000000):
>   if (is_prime(a) and is_prime(2**a-1))
>     print 2**a-1, " is a prime number"
> # Snipet off
> 
> Does not! Why ??


Don't use range, use xrange. The former will generate an actual list in
memory, which you usually  don't need - especially in for-loops as you
don't even have a reference on the list itself.

And I don't think that your change afflicts memory consumption at all. Must
be a coincidence.

Diez