How to add list to same variable in a for loop?

Question

I have a for loop with some calculations stored in a list. During second iteration of for loop, the earlier list is replaced with new one. I want to add new list to corresponding entries of old list:

for row in file:
    theValue = row.getValue("Value")

    if row.getValue("Value") == 20:
        ..................................
        a = ..............................
    b = [x*float(theValue) for x in a]

How to add "b" list into the list obtained during the second iteration in above for loop? For example:

b(1) = [2,3,4]
b(2) = [3,5,1]

so I want to get:

b = [5,8,5]

Do you want to add elements to the list or the list itself? And what do you mean by to corresponding entries of old list? — vidit
– vidit, Commented Oct 13, 2013 at 6:40
This question is somewhat confusing. Can you add an example? — Pandu
– Pandu, Commented Oct 13, 2013 at 6:46

warvariuc · Accepted Answer · 2013-10-13 07:11:32Z

1

Python 2.7.5+ (default, Sep 19 2013, 13:48:49) 
>>> a = [1, 2, 3]
>>> b = [0] * len(a)
>>> b
[0, 0, 0]
>>> for the_value in [4, 5]:
...     for i, x in enumerate(a):
...         b[i] += x * float(the_value)
... 
>>> b
[9.0, 18.0, 27.0]
>>>

answered Oct 13, 2013 at 7:11

warvariuc

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