a = [1,2,3] #create a list and make a reference to it
b = a #set b as a reference to the same list
a[1] = 4 #change one entry in the list
print(b) #prints [1,4,3] #because the object has changed
a = 123 #change a
print(b) #prints [1,4,3] #b has ceased to be a reference to the object