Will adding an instance of a class to a list copy the instance or just 'reference' it?

Will adding an instance of a class to a list copy the instance or just
'reference' it?

References

Reference NO 1

http://stackoverflow.com/questions/2106725/how-do-i-copy-an-instance-of-an-object

Reference NO 2

http://stackoverflow.com/questions/12101958/keep-track-of-instances-in-python

Reference NO 3

http://esug.org/data/Articles/Columns/EwingPapers/cvars&cinst_vars.pdf

Reference NO 4

http://docs.python.org/library/copy.html

Reference NO 5

http://phrogz.net/programmingruby/tut_classes.html

Reference NO 6

http://math.hws.edu/javanotes/c5/s2.html

Reference NO 7

http://en.wikipedia.org/wiki/Clone_(Java_method)

Reference NO 8

http://weka.sourceforge.net/doc.dev/weka/core/Instances.html