Changing one element of a 2-D list in python

Adwat · 06-05-2012, 07:16 PM

I have the following code:

a=[[0]*2]*3

print a

a[1][1]=2 print a

the output is: [[0,0],[0,0],[0,0]] [[0,2],[0,2],[0,2]]

Why is it changing all the elements of the list?

Shouldn't the output be:

[[0,0],[0,2],[0,0]]

What needs to be done if I just want to change one of the element?

Thanks for the help!

evo2 · 06-05-2012, 10:06 PM

Hi,

this is because everything (except floats, ints etc) are references in python. Your 3 element array contains three references to the same two element array.

Try declaring your array like:

Code:

a = [ [0]*2 for i in range(3) ]

Evo2.

colucix · 06-06-2012, 06:36 PM

Moved: This thread is more suitable in Programming and has been moved accordingly to help your thread/question get the exposure it deserves.