CODEWITHSUNDEEP
python
tree em
tree em

Reputation: 21781

finding divisors of N using a list comprehension

I have started to write some Python code. What I have is:

from math import *
def ex(N):        
    l = []
    sum = 0
    N = abs(int(N));
    for n in range(1,N):
        if N % n == 0:
            l.append(n)
            sum += n
    l.append(N) 
    print '  of '+str(N),l
    print 'SUM', (sum+N)

I don't know if this is good or bad, but it is what I have tried :)

Is it possible to replicate the behavior of my code with list comprehension? If so, how?

Upvotes: 0

Views: 2236

Answers (4)

initzero
initzero

Reputation: 852

You can use list comprehension to replace:

for n in range(1,N):
        if N % n == 0:
            l.append(n)

with:

[l.append(n) for n in range(1,N) if N % n == 0]

Whether it is good or bad, in this case, I'm not sure. I like to use them when I can, but for more complex cases sometimes I opt for the for loop for readability.

Edit: Sorry, maybe I should have given a complete example.

def ex(N):    
    l = []
    N = abs(int(N));
    [l.append(n) for n in range(1,N) if N % n == 0]
    l.append(N)
    print l
    print sum(l)

Upvotes: 0

nmichaels
nmichaels

Reputation: 51029

l = [n for n in range(1,N+1) if N % n == 0]
total = sum(l)

Upvotes: 6

Nicholas Riley
Nicholas Riley

Reputation: 44351

Very simply (this actually uses a generator expression rather than a list comprehension, if you don't need to keep the results).

def ex(N):
    N = abs(int(N))
    print 'SUM', sum(n for n in xrange(1, N + 1) if N % n == 0)

If you care about the list, then instead:

def ex2(N):
    N = abs(int(N))
    l = [n for n in xrange(1, N + 1) if N % n == 0]
    print '  of '+str(N),l
    print 'SUM', sum(l)

You might find the Dive Into Python 3 explanation of list comprehensions useful, or if you've got some free hours, try watching an introductory Python tutorial.

Upvotes: 5

Santiago Alessandri
Santiago Alessandri

Reputation: 6855

You can do it with list-comprehension:

def ex(N):
    N = abs(int(N))
    l = [n for n in range(1, N + 1) if N % n == 0]
    print '  of '+str(N),l
    print sum(l)

You will keep the n for each n in the range from 1 to N(inclusive) if the condition(N % n == 0) is true. You will keep the list in l and then the function sum calculates the sum of the list.

Whether it is good or bad using list comprehension is up to you, but it is usually used as it is efficient and compact. And if you don't need a list because you just need to use the values one after the other and only one time generators are recommended because they don't use memory.

Upvotes: 4

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