IceDust - 4 months ago 9

Python Question

I need to write a function where, for any list, each element in the list is added together and to see if it equals a constant.

For example:

`L = [1, 2, 3, 4]`

The sum of each element added together is

`1+2=3`

`1+3=4`

`1+4=5`

`2+3=5`

`2+4=6`

`3+4=7`

And then to test each of these results to a constant eg if the output = C where

`C = 3`

I am not allowed to use indexing here.

So far I am able to add the numbers in pairs along the list:

`def prize(L):`

possible = []

C = 4

prevprev = L.pop(0)

prev = L.pop(0)

print("initial", prevprev, prev)

for n in L:

i = prev + prevprev

prevprev = prev

prev = L.pop(0)

if i == C:

possible.append(i)

return possible

print("possible ", possible)

But for some reason this misses out the last 2 elements in the list when iterating over it.

Answer

I couldn't quite follow your code or explanation quite well, but I believe this does what you want. This is done without the `itertools`

module. Using it would produce a more compact code. This is done as an alternative to `itertools`

```
lst = [1, 2, 3, 4]
def prize(L):
pair_list = []
C = 4
# Creates a list of tuples (1, 2), (1, 3), etc
for x in L:
for y in L:
# if x != y | To prevent 1 + 1 and 2 + 2 (following example)
# (y, x) not in pair_list | Prevent inverted pairs
if x != y and x + y == C and (y, x) not in pair_list:
pair_list.append((x, y))
# Return list tuples that add to constant
return pair_list
print('Possible', prize(lst))
```

if you wish to use itertools then you would use

```
from itertools import combinations
def prize(L):
C = 4
return [(x, y) for x, y in combinations(L, 2) if x + y == C]
lst = [1, 2, 3, 4]
print('Possible', prize(lst))
```

Source (Stackoverflow)

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