List Comprehensions then summing with for-loop

Question

I'm relatively new to Python and have been told to create a list using list comprehension to only display even numbers between 0-100 then add all of those numbers together. I understand how to do it if it was just a regular list such as:

Total = 0
for x in range (0,101,2):
     Total += x

I have no idea what to do though with the comprehension. It makes no sense to me. This is what I have.

Total = 0 
x = [x for x in range (1001) if x % 2 ==0]


Total +=int(???)
print('The total is:', Total)

I don't know what to put in for the ??? or even if I'm going about this the right way. Any help would be great!

Edit: I forgot to mention it needs to be in a for loop. I don't know how to create the for loop and the comprehension list.

wrap it into `sum()` (which sums all values of a collection) — yedpodtrzitko, Jan 27 '17 at 17:36
There shouldn't be any difference. Replace the `range` in the first example with the comprehension. — Carcigenicate, Jan 27 '17 at 17:39

score 2 · Answer 1 · edited May 23 '17 at 12:24

2

sum

Looking at this answer :

sum([x for x in range(101) if x%2 == 0])
#=> 2550

for and comprehension

total = 0
for even in [i for i in range(101) if i%2 == 0]:
     total += even
total
#=> 2550

Direct formula

n = 100
(n/2)*(n/2+1)
#=> 2550

edited May 23 '17 at 12:24

Community

1
1

answered Jan 27 '17 at 17:40

Eric Duminil

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Tagc · Accepted Answer · 2017-01-27T17:43:47.883

1

To do it with list comprehensions:

print(sum([x for x in range(0,101,2)]))

But you can just do:

print(sum(range(0,101,2)))

The output in both cases is 2550.

So apparently your requirements are to use a list comprehension and a for loop? I'm a bit confused but are you asking for this?

even_terms = [x for x in range(0,101,2)]

total = 0
for x in even_terms:
    print(x)
    total += x

print('total:', total)

Output

0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
62
64
66
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
total: 2550

edited Jan 27 '17 at 17:43

answered Jan 27 '17 at 17:37

Tagc

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Yea, it has to be in a for-loop; I forgot to mention that. That's the part that's confusing me. – John Jan 27 '17 at 17:40
`[x for x in range(0,101,2)]` is just `range(0,101,2)`, right? – Eric Duminil Jan 27 '17 at 17:42
1

@EricDuminil The latter returns a generator, and so is the lazy equivalent of the former. If you iterate them both you'll get the same output though. – Tagc Jan 27 '17 at 17:44
Okay. I'm using Python 2 though, so I think `range` really is a list, as opposed to `xrange`. – Eric Duminil Jan 27 '17 at 17:46
@EricDuminil Ah, then yeah. – Tagc Jan 27 '17 at 17:48

score 0 · Answer 3 · answered Jan 27 '17 at 17:43

0

Total = reduce( lambda x, y: x + y, filter( lambda n: n % 2 == 0, range( 0, 101 )  )

or

Total = reduce( lambda x, y: x + y, range( 0, 101, 2 ) )

answered Jan 27 '17 at 17:43

Reaper

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score 0 · Answer 4 · answered Jan 27 '17 at 17:45

Your first example was correct. Both range and the list produced by the comprehension are iterable, so they both work in a for-loop. Just replace the range with the comprehension:

xs = [x for x in range (1001) if x % 2 ==0]

Total = 0
for x in xs:
     Total += x

print(Total)

score 0 · Answer 5 · answered Jan 27 '17 at 18:02

Using sum is probably the canonical method for iterating over a list comprehension when adding.

def calculate_sum_over_range(start, end, interval=2):
    return sum(_ for _ in range(start, end, interval))

print(calculate_sum_over_range(0, 101))

Good luck on your homework assignment.

List Comprehensions then summing with for-loop

5 Answers5

sum

for and comprehension

Direct formula