Sequential sum in list by python

Question

I have a table (list of lists) in python like: (Python 3)

packets = [[a, b, (0+a), (0+b)], [e, f, (0+a+e), (0+b+f)], [i, j, (0+a+e+i), (0+b+f+j)]]

The first column is the size of packets and the second column is time difference. I want to calculate the total size in third column and sum of time in fourth column.

My code was :

for c in range (1, len(packets)):
    packets[c][2] = packets[c-1][2] + packets[c][0]
    packets[c][3] = packets[c-1][3] + packets[c][1] 

but I got memoryerror as the size of packets is near a million.

Please suggest me a way to fix this the memory problem.

Answer 1

Try using the xrange function instead of range:

for c in xrange(1,len(packets)):
    packets[c][2]=packets[c-1][2]+packets[c][0]
    packets[c][3]=packets[c-1][3]+packets[c][1] 

https://docs.python.org/2/library/functions.html#xrange

Edit

If you can't use xrange, then make your own:

def myrange(start, end):
    while True:
        if start == end:
            break
        yield start
        start += 1

for i in myrange(1, 10):
    print i