def isPrime(n):
for i in range(2,n):
if n % i == 0:
return False
return True
def prime_finder(n):
numbers = list(range(2, n+1))
primes = []
for i in numbers:
if isPrime(i):
primes.append(i)
return primes
print(prime_finder(11))
Hey goran_021,
How does 2 get added to the primes list? Obviously 2 % 2 == 0 and 2 % 1 == 0. How do lines 3, 4 and 5 account for that?
I appreciate this isn’t specific to your code but I understood yours the most. Any help would be much appreciated.
Thanks
Hi.
See here :
for i in range(2,n):
if n % i == 0:
If we talk about num 2, then it’s range(2,2), and range from 2 to 2 is none. Because range goes from start(2) to end minus one(2 - 1), and that would be range from 2 to 1 which doesn’t exist so result is none instead of zero you would normally expect.
Take care:)
You are a legend, thank you so much!
1 Like
big code
def prime_finder(n):
foo = []
def isComposite(n2):
x = [True]
for i in range(1, n2 + 1):
if n2 % i == 0 and not(i == 1 or i == n2):
x.append(False)
return not(x[-1])
for i in range(1, n + 1):
if not(isComposite(i)) and not(i == 1 or i == 0):
foo.append(i)
return foo
for i2 in range(40):
print("{} {}\n".format(i2, prime_finder(i2)))
def prime_finder(n):
primes = []
for i in range(2,n+1):
print(i)
flag = False
for x in range(2,i):
if flag:
continue
if i % x == 0:
flag = True
if not flag:
primes.append(i)
return primes
print(prime_finder(11))
Using list comprehension
def prime_finder(n):
num_list = [num for num in range(2, n+1) if num>1 if all(num % y != 0 for y in range(2, num))]
return num_list
print(prime_finder(11))
from math import factorial
def prime_finder(n):
# Write your code here
primes = []
for nums in range(2, n+1):
fact = factorial(nums-1)+1
if fact%nums == 0:
primes.append(nums)
return primes
print(prime_finder(11))
here’s my solution using wilsons’s theorem 
1 Like
def prime_finder(n):
# Write your code here
def is_prime(m):
for j in range(2,m):
if m%j == 0: return False
return True
prime_list = []
for i in range(2, n+1):
if is_prime(i): prime_list.append(i)
return prime_list
print(prime_finder(100))
def prime_finder(n):
# Write your code here
prime_n = []
for i in range(2,n+1):
prime_test = []
for j in range(2,i+1):
if i%j == 0:
prime_test.append(j)
if len(prime_test) == 1:
prime_n.append(i)
return prime_n
print(prime_finder(11))
I ended up using a Sieve of Eratosthenes. It completes in about 12 microseconds for prime_finder(100) according to IPython’s %timeit function:
def prime_finder(n):
# Write your code here
if n < 2:
return []
elif n == 2:
return [2]
elif n < 5:
return [2, 3]
# For n above 4, use a sieve of Eratosthenes.
RANGE_MAX = n + 1
primes = [True for i in range(RANGE_MAX)]
# 0 and 1 are not prime.
primes[0] = False
primes[1] = False
# Set all multiples of 2 to False.
for n in range(4, RANGE_MAX, 2):
primes[n] = False
# Loop through all odd numbers up to the square root of RANGE_MAX.
# If the number is prime, set all of its odd multiples to False.
for i in range(3, int(RANGE_MAX**0.5) + 1, 2):
if primes[i]:
for j in range(i*i, RANGE_MAX, i*2):
if primes[j]:
primes[j] = False
# Return the primes using list comprehension.
# This is more efficient than appending to a list.
return [i for i, prime in enumerate(primes) if prime]
print(prime_finder(11))
print(prime_finder(49))
‘’’
1. def prime_finder(n):
2. if n < 0:
3. raise ValueError('n must be positive.')
4. if n < 2:
5. return []
6. primes = [2]
7. if n == 2:
8. return primes
9. # a prime number > 2 must be odd and indivisible by all primes less than it
10. for i in range(3, n+1, 2):
11. isprime = True
12. for j in primes:
13. if i % j == 0:
14. isprime = False
15. if isprime:
16. primes.append(i)
17. return primes
18. print(prime_finder(11))
def prime_finder(n):
# Write your code here
prime_num = [] # store prime numbers
# loop to iterate over values to n
for i in range(2,n+1):
count = 0 # keep track of evenly divisble values
for j in range(2,i):
print('i= '+ str(i) + ', j = ', str(j) + ' mod_val = ' + str(i%j))
# if there is any time a divisble is found, add to count and break loop
if i % j == 0:
count += 1
break
if count == 0:
prime_num.append(i)
return prime_num
print(prime_finder(11))
Lots of interesting approaches here. I wanted to find the quickest approach. I used the break method that others above have used. Is there a quicker way to approach this?
def prime_finder(n):
list = []
for n in range(1,n+1):
if n > 1:
for i in range(2,n):
if (n % i) == 0:
break
else:
list.append(n)
return list
print(prime_finder(11))
This is how I solved it.
Not very efficient but gets there eventually
def find_prime(n):
#setting a list where the first number is range[2] of n, since 0 and 1 will never be prime and you can't divide by zero
lst = list(range(n + 1))
lst_no_one = lst[2:]
almost_prime = []
#iterating through the list twice and appending to almost_prime if the % operation returns 0
for num in lst_no_one:
for num2 in lst_no_one:
if num % num2 == 0:
almost_prime.append(num)
#if the number is only one time at the list it is prime, so making a dict to check num frequency
dict_prime = {}
for num in almost_prime:
if num in dict_prime:
dict_prime[num] += 1
else:
dict_prime[num] = 1
#appending to prime list the keys with value of one
prime = []
for key, value in dict_prime.items():
if value == 1:
prime.append(key)
return prime
print(find_prime(10))
Well, that is some elegant code right there…
def prime_finder(n):
Write your code here
Start with 3 and already add 2 in the list
number = 3
list of prime numbers till “n”
prime_numbers =
prime_numbers.append(2)
while number <= n:
prime = False
test = 2
while test < number:
if number % test == 0:
prime = True
test += 1
if prime == False:
prime_numbers.append(number)
number += 1
return prime_numbers
print(prime_finder(11))
Should have use the break statement!
import math
def prime_finder(n):
primes = list(range(2, n+1))
print("List to analize : \n", primes, "\n")
list_to_analize = []
for i in range(2,n+1):
list_to_analize = list(range(2, math.ceil(i/2)+1))
print("Analizing ", i, "with ", list_to_analize)
for j in range(2, math.ceil(i/2)+1):
print("dividing ", i ,"with ", j)
if i%j == 0 and i != j:
print("Removing ", i)
primes.remove(i)
break
print("primes after this iteration ", primes, "\n")
return primes
print(prime_finder(11))
def is_prime(n):
if (n <= 3) :
return "Prime"
for i in range(2, n+1 // 2):
if n % i == 0:
return "Not Prime"
else:
return "Prime"
def prime_finder(n):
# Write your code here
if n > 1:
results = []
for i in range(2, n+1):
if is_prime(i) == "Prime":
results.append(i)
return results
print(prime_finder(11))