Hey, big thanks to you and Gabriel for replying. I couldn't quite follow what you did yet. What is this 'gimpy' thing and where can I read about it? In response:
First: Heh, I'm a little embarrassed I didn't notice this. I thought 'I only need to check up to half' but it didn't occur that base**2 was more than 1/2 candidate. Second: I don't quite follow this. Third: Yeah, I found that bug just before, and because of, posting. Fourth: I used the incrementing command and incremented candidates by two to check only odds and now the program is a lot faster. Thanks a lot for yall's replies. Three more things before I go. What is the square root function in python? I couldn't find the fact.py demo script. I didn't mean return I meant 'continue'. Mensanator wrote: > On Mar 17, 7:03 pm, Benjamin Serrato <[EMAIL PROTECTED]> > wrote: >> I Found It!! The following was a post asking for help finding a bug. I >> thought I needed help with my syntax, but just before sending I found >> the bug on line 13. Line 13 should read: "base = 2". I would still >> appreciate any comments on my program. Maybe there is a better way to do >> it that I didn't think about. I know it's not that interesting but it's >> my first one. >> >> [post] >> I'm almost halfway through an online tutorial I found on the python.org >> site and decided to stop and write a program for myself. I got it in my >> head to write a program to print all the primes; the idea came from >> another tutorial. The program prints some non-prime numbers. In a >> comparison to lists of primes the program prints eight non-primes for >> numbers less than 150. Those numbers are [27,35,87,95,119,123,143,147]. >> Here is the program. >> >> base = 2 >> candidate = 3 >> >> while True: >> while candidate % base != 0: >> base = base + 1 >> if base > (candidate / 2): >> print candidate >> candidate = candidate + 1 >> base = 2 >> else: >> candidate = candidate + 1 >> >> The following is a rundown of the program. >> >> candidate: A possible prime number. >> base: Start point for divisibility testing. >> outer while loop: Causes the program to loop. >> inner while loop: Obviously, checks if 'candidate' mod 'base' equals >> zero. If not base is incremented by one then 'if loop'. >> if loop: After base has been incremented this checks whether all the >> possible divisors have been used up. If they have then 'candidate' must >> be prime. So, candidate is printed, a new candidate is chosen and the >> base is reset. >> else loop: If 'candidate' mod 'base' equals zero, then 'candidate' is >> not prime and a new candidate is chosen. >> >> I realize yall probably didn't need all that. >> >> At first I tried to use 'return' on the 'else' block to cause the >> program to loop, but I don't understand 'return' yet and that didn't >> work. So, I put the rest into another while loop and was really happy to >> find it worked but the program prints some non-prime numbers. >> >> Thanks, Benjamin Serrato >> >> P.S. What is the chance I'll get spam for using my real email address? I >> currently don't get any so... >> [/post] > > Several items. > > First, you don't need to check base larger than sqrt(candidate). > > Second, see comments following dc. > > Third, you need to add base = 2 to end of program, otherwise next > candidate starts base where previous candidate left off. > > Fourth, use +=1 to increment. > > Finally, throw this away and use gmpy. :-) > > > import gmpy # for Quality Assurance > base = 2 > candidate = 3 > p = 0 # prime count > while p<100: # limit the loop to 100 primes > while candidate % base != 0: > base += 1 > #if base > (candidate / 2): > if base > (gmpy.sqrt(candidate)): # only need to test to > sqrt(candidate) > dc = divmod(candidate,2) # remainder==0 gives false > primes > if dc[1]==1: > # > # the gmpy functions are for QA, verifies that what you call a > prime > # really is one and the next_prime makes sure you don't skip > any > # these can be removed once working > # > print > candidate,gmpy.is_prime(candidate)>0,gmpy.next_prime(candidate) > p += 1 > candidate += 1 > base = 2 > else: > candidate += 1 # false prime, reset > base = 2 > else: > candidate += 1 > base = 2 # failure to reset causes false > primes > > ## 3 True 5 > ## 5 True 7 > ## 7 True 11 > ## 11 True 13 > ## 13 True 17 > ## 17 True 19 > ## 19 True 23 > ## 23 True 29 > ## 29 True 31 > ## 31 True 37 > ## 37 True 41 > ## 41 True 43 > ## 43 True 47 > ## 47 True 53 > ## 53 True 59 > ## 59 True 61 > ## 61 True 67 > ## 67 True 71 > ## 71 True 73 > ## 73 True 79 > ## 79 True 83 > ## 83 True 89 > ## 89 True 97 > ## 97 True 101 > ## 101 True 103 > ## 103 True 107 > ## 107 True 109 > ## 109 True 113 > ## 113 True 127 > ## 127 True 131 > ## 131 True 137 > ## 137 True 139 > ## 139 True 149 > ## 149 True 151 > ## 151 True 157 > ## 157 True 163 > ## 163 True 167 > ## 167 True 173 > ## 173 True 179 > ## 179 True 181 > ## 181 True 191 > ## 191 True 193 > ## 193 True 197 > ## 197 True 199 > ## 199 True 211 > ## 211 True 223 > ## 223 True 227 > ## 227 True 229 > ## 229 True 233 > ## 233 True 239 > ## 239 True 241 > ## 241 True 251 > ## 251 True 257 > ## 257 True 263 > ## 263 True 269 > ## 269 True 271 > ## 271 True 277 > ## 277 True 281 > ## 281 True 283 > ## 283 True 293 > ## 293 True 307 > ## 307 True 311 > ## 311 True 313 > ## 313 True 317 > ## 317 True 331 > ## 331 True 337 > ## 337 True 347 > ## 347 True 349 > ## 349 True 353 > ## 353 True 359 > ## 359 True 367 > ## 367 True 373 > ## 373 True 379 > ## 379 True 383 > ## 383 True 389 > ## 389 True 397 > ## 397 True 401 > ## 401 True 409 > ## 409 True 419 > ## 419 True 421 > ## 421 True 431 > ## 431 True 433 > ## 433 True 439 > ## 439 True 443 > ## 443 True 449 > ## 449 True 457 > ## 457 True 461 > ## 461 True 463 > ## 463 True 467 > ## 467 True 479 > ## 479 True 487 > ## 487 True 491 > ## 491 True 499 > ## 499 True 503 > ## 503 True 509 > ## 509 True 521 > ## 521 True 523 > ## 523 True 541 > ## 541 True 547 > ## 547 True 557 -- http://mail.python.org/mailman/listinfo/python-list
