puzzling python index error

Question

Here is a piece of python code ("result" is a nested list created before)

for i in range(len(result)-1):
    try:
        result[i][3]=0
        result[i+i][0]=0
    except IndexError:
        print "fail", result[i][3], result[i+1][0], i, len(result)
return result

which, to my astonishment, quite often prints "fail" (with non-revealing values for i, len(result), e.g. 24, 31). How can

result[i][3]=0
result[i+i][0]=0

produce the IndexError exception, if

print result[i][3], result[i+1][0]

does not?

Martijn Pieters · Accepted Answer · 2012-10-15 20:18:49Z

9

You are accessing the index i + i, not i + 1:

result[i+i][0]=0

This means that by the time you reach i // 2 + 1 you have an index error, whatever the size of your list.

answered Oct 15, 2012 at 20:18

Martijn Pieters

1.1m326 gold badges4.2k silver badges3.4k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

puzzling python index error

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related