Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>There are some problems:</p> <ul> <li>Why do you print out count when it didn't divide by x? It doesn't mean it's prime, it means only that this particular x doesn't divide it</li> <li><code>continue</code> moves to the next loop iteration - but you really want to stop it using <code>break</code></li> </ul> <p>Here's your code with a few fixes, it prints out only primes:</p> <pre><code>import math def main(): count = 3   while True: isprime = True   for x in range(2, int(math.sqrt(count) + 1)): if count % x == 0: isprime = False break   if isprime: print count   count += 1 </code></pre> <p>For much more efficient prime generation, see the Sieve of Erastothenes, as others have suggested. Here's a nice, optimized implementation with many comments:</p> <pre><code># Sieve of Eratosthenes # Code by David Eppstein, UC Irvine, 28 Feb 2002 # http://code.activestate.com/recipes/117119/ def gen_primes(): """ Generate an infinite sequence of prime numbers. """ # Maps composites to primes witnessing their compositeness. # This is memory efficient, as the sieve is not "run forward" # indefinitely, but only as long as required by the current # number being tested. # D = {}   # The running integer that's checked for primeness q = 2   while True: if q not in D: # q is a new prime. # Yield it and mark its first multiple that isn't # already marked in previous iterations # yield q D[q * q] = [q] else: # q is composite. D[q] is the list of primes that # divide it. Since we've reached q, we no longer # need it in the map, but we'll mark the next # multiples of its witnesses to prepare for larger # numbers # for p in D[q]: D.setdefault(p + q, []).append(p) del D[q]   q += 1 </code></pre> <p>Note that it returns a generator.</p>
    singulars
    1. This table or related slice is empty.
    1. POSimple Prime Generator in Python
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USAlice Purcell
    1. USEli Bendersky
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POSimple Prime Generator in Python
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThis sieve is very terse. Where did it come from?
      singulars
      1. PO
      1. USSingleNegationElimination
    2. COThat's a really excellent implementation of the Sieve. I've never seen it applied to indefinite ranges before, but it's obvious in retrospect.
      singulars
      1. PO
      1. USNick Johnson
    3. COThe dictionary operation is time-consuming, if you have enough memory, you had better save all the numbers in the memory instead of use a dictionary to add and remove elements dynamically.
      singulars
      1. PO
      1. USxiao 啸
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload