Question

I have list of 10 elements having a tuple of 2 elements I want to add to each tuple a value but when i write the following code to do so it seems that cumulative sum is caluculated . How is this happening. please help

# -*- coding: utf-8 -*-
i=0
k=10
count=[]
value=[1,2]
while i < k:
  count.append(value)
  i=i+1
t=[10,2]
i=0
#for item in count:
  #print item
while i <(len(count)):
  count[i][0]+=t[0];
  count[i][1]+=t[1];
  i+=1;

for item in count:
  print item

outpus is coming out to be

[101, 22]
[101, 22]
[101, 22]
[101, 22]
[101, 22]
[101, 22]
[101, 22]
[101, 22]
[101, 22]
[101, 22]

where as i expected it to be

[11, 4]
[11, 4]
[11, 4]
[11, 4]
[11, 4]
[11, 4]
[11, 4]
[11, 4]
[11, 4]
[11, 4]

Answer 1

That’s because you actually have a list of ten references to the same (single) 2-item list. You are repeatedly adding to that same list in the second loop. You really want a new instance of a the sublist (and what you really have is a mutable list, not a tuple).

You could do this:

while i < k:
  count.append(value[:])
  i=i+1

To get new copies of the embedded list.