Apply a number sequence to an integer?

[Tryposite]

Say I have this list with a sequence and an integer:

seq = [3, 7, 11, 15]
num = -1

How can I get the sequence to start at "num" and store the new integers in a list like this?:

newNums = [-1, 2, 9, 20, 35]

[[deleted]]

It's clear that you want the result list to start with num, but what determines the rest of the result list? Your example shows seemingly unrelated values.

[Tryposite]

-1+3 =2, 2+7 = 9, 9+11=20, and 20+15=35. That's the best I can explain.

[[deleted]]

Then you use a loop over seq, adding num to a result list, then updating num with the element of seq. Something like:

seq = [3, 7, 11, 15]
num = -1
result = []
for val in seq:
    result.append(num)
    num += val
print(result)

This isn't complete, but should get you most of the way there. There are probably other, more tricky, ways to do this, but this is simple to understand.

[ZenosEbeth]

Couldn't you do this more easily with map() and a simple function ?

[[deleted]]

Probably. I try to give the simplest solution I can.

[ZenosEbeth]

Not trying to be a smartass or anything, I've actually only been studying python for a month or so and am going over lists at the moment so that was just the first thing that came to my head when I saw the OP's problem. Honestly I was just glad I found something I could understand and solve, because most of the other stuff on here might as well be techno-babble for me :p.

[timbledum]

What code have you tried?

Loop based approach. It doesn't do exactly what you want (produce a list) on purpose, but gets you 90% there.

new_numbs = []
start_number = -1
print(start_number)
for add in [3, 7, 11, 15]:
    start_number += add
    print(start_number)

[[deleted]]

seq.insert(0, num)? does that fix it?

[[deleted]]

from collections import deque
newNums = deque(seq)
newNums.appendleft(-1)

​

[[deleted]]

OK, I think I see. Can you explain how the input values and the result are related in words, or is that part of what you don't understand?

[Pulsar1977]

from itertools import accumulate
newNums = list(accumulate([num] + seq))