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Python prime numbers

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  Python prime numbers Panagiotis Anastasiou <panast24@gmail.com> - 2014-02-01 07:33 -0800
    Re: Python prime numbers Larry Martell <larry.martell@gmail.com> - 2014-02-01 10:50 -0500
    Re:Python prime numbers Dave Angel <davea@davea.name> - 2014-02-01 16:59 -0500
    Re:Python prime numbers Dave Angel <davea@davea.name> - 2014-02-01 17:07 -0500
    Re: Python prime numbers Wiktor <look@signature.invalid> - 2014-02-02 00:34 +0100

#65220 — Python prime numbers

Hi i'm new in programming and in python and i have an assignment that i cant complete. I have to Write a Python program to compute and print the first 200 prime numbers. The output must be formatted with a title and the prime numbers must be printed in 5 properly aligned columns . I have used this code so far :

numprimes = raw_input('Prime Numbers  ')
count = 0
potentialprime = 2

def primetest(potentialprime):
    divisor = 2
    while divisor <= potentialprime:
        if potentialprime == 2:
            return True
        elif potentialprime % divisor == 0:
            return False
            break
        while potentialprime % divisor != 0:
            if potentialprime - divisor > 1:
                divisor += 1
            else:
                return True

while count < int(numprimes):
    if primetest(potentialprime) == True:
        print potentialprime
        count += 1
        potentialprime += 1
    else:
        potentialprime += 1

but i get the result in a single column . How can i get it in 5 rows? Can someone help please

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#65224

[Multipart message — attachments visible in raw view] — view raw

On Saturday, February 1, 2014, Panagiotis Anastasiou <panast24@gmail.com>
wrote:

> Hi i'm new in programming and in python and i have an assignment that i
> cant complete. I have to Write a Python program to compute and print the
> first 200 prime numbers. The output must be formatted with a title and the
> prime numbers must be printed in 5 properly aligned columns . I have used
> this code so far :
>
> numprimes = raw_input('Prime Numbers  ')
> count = 0
> potentialprime = 2
>
> def primetest(potentialprime):
>     divisor = 2
>     while divisor <= potentialprime:
>         if potentialprime == 2:
>             return True
>         elif potentialprime % divisor == 0:
>             return False
>             break
>         while potentialprime % divisor != 0:
>             if potentialprime - divisor > 1:
>                 divisor += 1
>             else:
>                 return True
>
> while count < int(numprimes):
>     if primetest(potentialprime) == True:
>         print potentialprime
>         count += 1
>         potentialprime += 1
>     else:
>         potentialprime += 1
>
> but i get the result in a single column . How can i get it in 5 rows? Can
> someone help please
>


If you put a comma at the end of the print statement it will suppress the
newline.

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#65239

 Panagiotis Anastasiou <panast24@gmail.com> Wrote in message:
> Hi i'm new in programming and in python and i have an assignment that i cant complete. I have to Write a Python program to compute and print the first 200 prime numbers. The output must be formatted with a title and the prime numbers must be printed in 5 properly aligned columns . I have used this code so far :
> 
> numprimes = raw_input('Prime Numbers  ')
> count = 0
> potentialprime = 2
> 
> def primetest(potentialprime):
>     divisor = 2
>     while divisor <= potentialprime:
>         if potentialprime == 2:
>             return True
>         elif potentialprime % divisor == 0:
>             return False
>             break
>         while potentialprime % divisor != 0:
>             if potentialprime - divisor > 1:
>                 divisor += 1
>             else:
>                 return True
> 
> while count < int(numprimes):
>     if primetest(potentialprime) == True:
>         print potentialprime
>         count += 1
>         potentialprime += 1
>     else:
>         potentialprime += 1
> 
> but i get the result in a single column . How can i get it in 5 rows? Can someone help please
> 


-- 
DaveA

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#65240

 Panagiotis Anastasiou <panast24@gmail.com> Wrote in message:
> Hi i'm new in programming and in python and i have an assignment that i cant complete. I have to Write a Python program to compute and print the first 200 prime numbers. The output must be formatted with a title and the prime numbers must be printed in 5 properly aligned columns . I have used this code so far :
> 
> numprimes = raw_input('Prime Numbers  ')
> count = 0
> potentialprime = 2
> 
> def primetest(potentialprime):
>     divisor = 2
>     while divisor <= potentialprime:
>         if potentialprime == 2:
>             return True
>         elif potentialprime % divisor == 0:
>             return False
>             break
>         while potentialprime % divisor != 0:
>             if potentialprime - divisor > 1:
>                 divisor += 1
>             else:
>                 return True
> 

There are several things wrong with this function,  and it's
 redundant enough that maybe none of them matter.  I'd test it
 carefully. 

> while count < int(numprimes):
>     if primetest(potentialprime) == True:
>         print potentialprime
>         count += 1
>         potentialprime += 1
>     else:
>         potentialprime += 1
> 
> but i get the result in a single column . How can i get it in 5 rows? Can someone help please
> 

As has been pointed out,  you can use a trailing comma to suppress
 the implied newline for each print. 
Then you can add it back in every five items by checking count.

But you have a bigger problem,  lining up the columns.  Try using
 the string modulus operator, or 'format'.

-- 
DaveA

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#65244

On Sat, 1 Feb 2014 07:33:47 -0800 (PST), Panagiotis Anastasiou wrote:

> Hi i'm new in programming and in python and i have an assignment that
> i cant complete. I have to Write a Python program to compute and print the 
> first 200 prime numbers. The output must be formatted with a title and the 
> prime numbers must be printed in 5 properly aligned columns . I have used this 
> code so far :

  Hi,
  try out this code:

for i in range(200):
   print '{0:>5}'.format(i),
   if (i-4) % 5 == 0:
       print

  Or maybe, if it's still unclear, try execute these lines:

print 'Hello {0}'.format('world')
print '|{0:>30}|'.format('right')
print '|{0:<30}|'.format('left')
print '|{0:^30}|'.format('center')
print '|{0:>16}|'.format('right'),
print '|{0:<16}|'.format('left'),
print '|{0:^16}|'.format('center')

  But still, it might be hard to implement this printing for..in loop while
you're verifying primes (in another loop), so maybe think about getting first
200 primes in while loop like you do (and only storing them in a list), and
then printing them out from this list in external for..in loop.



  Now, to your primetest() function. It may be good for small primes, but try
to verify with it, if 832475734579 is a prime. :)

> def primetest(potentialprime):
>     divisor = 2
>     while divisor <= potentialprime:

  First of all, see that you rarely use this loop - you check this condition at
most two times. You end up for good in the second while loop.

>         if potentialprime == 2:
>             return True
>         elif potentialprime % divisor == 0:
>             return False
>             break

  'break' after return is redundant - never executes

>         while potentialprime % divisor != 0:
>             if potentialprime - divisor > 1:
>                 divisor += 1
>             else:
>                 return True

  So, this is your main loop. Very inefficient. Think about that:
a) do you really have to check divisors up to the potentialprime? 
   Maybe there is a point, where you may say, that you've checked all 
   possibilities? Remember that a * b = b * a 
b) do you really have to check every divisor? I mean, increasing 
   it by 1 in every step?

-- 
Best regards,     Wiktor Matuszewski
'py{}@wu{}em.pl'.format('wkm', 'ka')

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