def nochange(y): y = 1x = 2nochange(x)print x # prints 2def nochange(y): y = ['hello']x = ['not hello']nochange(x)print x # prints ['not hello']# What is happening in the above is the following,## You are creating a list which has the content ['not hello'] and then telling# the varible 'x' to point at this list.## When you call nochange, the y argument is set to point to what x is also# pointing to. The next line then tells y to point somewhere else!# So why does the following work?def changeme(y): y.append('hello')x = []changeme(x)print x # prints ['hello']# You created an empty list and tell the varible 'x' to point to this list.# You then call the changeme function, the y argument is set to point to what x# is also pointing to. Then you say "call the append function on this thing# which y points to".## The append function then changes the contents of the object that y and x are# both pointing too.# So why doesn't the following workdef changeme(y): y += 1x = 2changeme(x)print x # prints 2# The reason this does not work is because an integer is immutable. You can not# change an int object. ## This means that y += 1 is mapped to y = y+1## Which means, take the object at y, add one and assign y the resulting object.#