Agarwal Prega - 4 months ago 36

Python Question

I am struck and need help with this..

I want to find the sum of prime numbers from a given list of integers. Here are a few test cases for the same.

`n([3,3,1,13])`

19

n([2,4,6,9,11])

13

n([-3,0,1,6])

0

The Code that I have written is as follows but it fails with the test cases above..

`def sumprimes(n):`

sum1 = 0

for i in range(0,len(n)):

num = n[i]

if num > 1:

for j in range(2, int(num**0.5)+1):

if num%j != 0:

sum1 = sum1 + num

else:

sum1 = 0

return(sum1)

Answer

This part is wrong:

```
for j in range(2, int(num**0.5)+1):
if num%j != 0:
sum1 = sum1 + num
```

you are summing `num`

for each number in the range that didn't divide.
you should sum just if **all** of them didn't divide.

Simple way to do this is:

```
prime = True
for j in range(2, int(num**0.5)+1):
if num%j == 0:
prime = false
break
if prime:
sum1 = sum1 + num
```

Or in a more *pythonic* way using all():

```
if all(num%j != 0 for j in range(2, int(num**0.5)+1)):
sum1 = sum1 + num
```