Try... except....Try again?

MRAB python at
Fri Jul 17 09:17:20 EDT 2009

Xavier Ho wrote:
> I have a simple class that generates prime numbers, using memorisation 
> and iteration to generate the next prime number.
> In the class, I have defined a function that gives, say, the 5th prime 
> number. Or the 1000th, it's still very fast. But the code isn't what I 
> really like.
>     def nPrime(self, n):
>         "Returns nth prime number, the first one being 2, where n = 0. 
> When n = 1, it returns 3."
>         while True:
>             try:
>                 return self.primes[n]
>             except:
> The next() function generates the next prime, and appends it into 
> primes. This way, it keeps trying to append until the nth prime 
> requested exist, and returns it.
> My problem is that it's a "While True" loop, which I get a lot of "Don't 
> do it!" In the light of making the code better, what could I do?
I wouldn't use a bare "except". What if you had written "prims" instead
of "primes"? It would catch AttributeError and produce the next prime, 
repeating until it ran out of memory.

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