Little novice program written in Python

[Steve Holden]

Rogério Brito wrote:
> Hi, All.
> 
> I'm just getting my feet wet on Python and, just for starters, I'm 
> coding some elementary number theory algorithms (yes, I know that most 
> of them are already implemented as modules, but this is an exercise in 
> learning the language idioms).
> 
> As you can see from the code below, my background is in C, without too 
> much sophistication.
> 
> What I would like is to receive some criticism to my code to make it 
> more Python'esque and, possibly, use the resources of the computer in a 
> more efficient way (the algorithm implemented below is the Sieve of 
> Eratosthenes):
> 
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> #!/usr/bin/env python
> 
> n = int(raw_input())
> a = [i for i in range(0,n+1)]
> a[1] = 0  # not a prime
> prime = 1 # last used prime
> finished = False
> 
> while (not finished):
>     prime = prime + 1
>     # find new prime
>     while prime*prime <= n and a[prime] == 0:
>     prime += 1
>     # cross the composite numbers
>     if prime*prime <= n:
>     j = 2*prime
>     while j <= n:
>         a[j] = 0
>         j += prime
>     else:
>     finished = True
> 
> # print out the prime numbers
> i = 2
> while i <= n:
>     if a[i] != 0:
>     print a[i]
>     i += 1
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 
> Thank you for any help in improving this program,
> 
Your Python is actually pretty good - if Raymond Hettinger pronounces it 
OK then few would dare to disagree.

As for your English, though, the word you sought was "Pythonic" (not 
that you will ever find such a word in Webster's dictionary). To suggest 
that your code is Pythonesque would mean you found it farcical or 
ridiculous (like a Monty Python sketch), which it clearly is not.

Another wrinkle you might consider is simply printing the primes out as 
they are generated rather than doing the printing in a separate loop, 
though whether that approach would be preferable in "real life" would 
depend on the application, of course.

regards
  Steve

PS: I think either my mailer or yours has mangled the indentation.
-- 
Steve Holden        +1 571 484 6266   +1 800 494 3119
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