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'int' object has no attribute 'is_prime'

asked 2018-04-09 09:43:39 -0500

Faisal gravatar image

updated 2018-04-09 09:48:13 -0500

Hi ... I am wondering why this code is not working

for number in range(20,30):
  if number.is_prime():
    print number

I got this error in Cocalc

Error in lines 1-3
Traceback (most recent call last):
  File "/cocalc/lib/python2.7/site-packages/smc_sagews/", line 1013, in execute
    exec compile(block+'\n', '', 'single') in namespace, locals
  File "", line 2, in <module>
AttributeError: 'int' object has no attribute 'is_prime'

However, it works when I change the code to

for number in range(20,30):
    if is_prime(number):
        print number
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1 answer

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answered 2018-04-09 10:22:34 -0500

slelievre gravatar image

updated 2018-04-10 08:54:01 -0500

This is because range spits out Python integers, and not Sage integers.

Python integers are "machine integers", that are designed to be fast, but can only be used for standard operations, and don't know about the rich structure of the ring of integers.

You could use srange, which works like range but gives you Sage integers.

If you use range, then use ZZ(number).is_prime() to first convert the numbers to integers before applying the .is_prime() method.

What is_prime(number) does is to try and apply the .is_prime() method if it is available, and otherwise first convert the number to a Sage integer, then apply the .is_prime() method.

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Thank you @slelievre so much for your detailed answer..

Faisal gravatar imageFaisal ( 2018-04-13 02:06:17 -0500 )edit

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Asked: 2018-04-09 09:43:39 -0500

Seen: 42 times

Last updated: Apr 10