CODEWITHSUNDEEP
pythonmathlist-comprehension
JavaSa
JavaSa

Reputation: 6241

Finding prime numbers using list comprehention

I was trying to generate all prime numbers in range x to y. I tried simple example first: range(10,11) which means to check if 10 is a prime number:
Here is my code:

prime_list = [x for x in range(10, 11) for y in range(2,x) if x % x == 0 and x % 1 == 0 and x % y != 0]

I know that the thing is missing the option to tell the expression that x%y != 0 should be checked for all y in range (2,x) and return true if and only if all have met this condition.

How do we do that?

Upvotes: 14

Views: 46591

Answers (9)

falsetru
falsetru

Reputation: 369094

Use all to check all elements (from 2 upto x-1) met conditions:

>>> [x for x in range(2, 20)
     if all(x % y for y in range(2, x//2))]
[2, 3, 5, 7, 11, 13, 17, 19]

Upvotes: 36

DrSanjay Bhakkad
DrSanjay Bhakkad

Reputation: 19

Program to find prime numbers within a given range using list comprehensions:

min = 10

max = 100

primes = [num for num in range(min,max) if 0 not in [num%i for i in range(2,num//2)]]

print (primes)

Upvotes: 2

Deepeshkumar
Deepeshkumar

Reputation: 443

Here is an example for generating prime numbers up to 1000! The same can be used for any range.

primes = [num for num in range(2,1000) if True not in [True for divisor in range(2,(int(num/2)+1)) if num % divisor == 0 and num != 2]]

Upvotes: 0

Gaurav Tiwari
Gaurav Tiwari

Reputation: 1

Use this code for finding prime numbers upto given range.

>>> lower = int(input("Enter lower range: "))

>>> upper = int(input("Enter upper range: "))

>>> [x for x in range(lower, upper+1) if x>1 if all(x % y != 0 for y in range(2, x))]

Upvotes: 0

Kashvi
Kashvi

Reputation: 1

The code can be shortened to one line using lambda function:

prime = list(filter(lambda x:all(x % y !=0 for y in range(2,x)),range(2,11)))
print(prime)

Upvotes: 0

Cibas Mec
Cibas Mec

Reputation: 41

You could optimize more using the concept of the square root so as not to iterate throughout the list and calculate the prime numbers faster in the following way!!

import math
[x for x in range(2, 21) if  all(x % y != 0 for y in range(2, int(math.sqrt(x + 1)) ) )]

Upvotes: 3

NeoWang
NeoWang

Reputation: 18513

The version with filter:

filter(lambda x:all(x % y != 0 for y in range(2, x)), range(2, 13))

Upvotes: 1

bad_keypoints
bad_keypoints

Reputation: 1400

@falsetru's answer is correct. But also, attention should be paid to optimized code. As someone said in the the comments in Kasra's answer

In [227]: %timeit [x for x in range(4, 1000) if all(x % y != 0 for y in range(2, int(m.sqrt(x)) + 1))]
100 loops, best of 3: 2.08 ms per loop

In [228]: %timeit [x for x in range(4, 1000) if all(x % y != 0 for y in range(2, int(m.sqrt(x)) + 1))]
100 loops, best of 3: 2.09 ms per loop

In [229]: %timeit [x for x in range(4, 1000) if all(x % y != 0 for y in range(2, x-1))]
100 loops, best of 3: 10.4 ms per loop

In [230]: %timeit [x for x in range(4, 1000) if all(x % y != 0 for y in range(2, x-1))]
100 loops, best of 3: 10.3 ms per loop

Upvotes: 1

div
div

Reputation: 573

One way using set comprehension can be

list(set(range(2,11)) - {x for x in range(11) for y in range(2,x) if x%y == 0})

Upvotes: 3

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