Test 1
>>> a = [1,2,3] # set a to point to a list [1, 2, 3]
>>> b = a # set b to what a is currently pointing at
>>> a = [] # now you set a to point to an empty list
# Step 1: A --> [1 2 3]
# Step 2: A --> [1 2 3] <-- B
# Step 3: A --> [ ] [1 2 3] <-- B
# at this point a points to a new empty list
# whereas b points to the original list of a
Test 2
>>> a = [1,2,3] # set a to point to a list [1, 2, 3]
>>> b = a # set b to what a is currently pointing at
>>> del a # delete the reference from a to the list
# Step 1: A --> [1 2 3]
# Step 2: A --> [1 2 3] <-- B
# Step 3: [1 2 3] <-- B
# so a no longer exists because the reference
# was destroyed but b is not affected because
# b still points to the original list
Test 3
>>> a = [1,2,3] # set a to point to a list [1, 2, 3]
>>> b = a # set b to what a is currently pointing at
>>> del a[:] # delete the contents of the original
# Step 1: A --> [1 2 3]
# Step 2: A --> [1 2 3] <-- B
# Step 2: A --> [ ] <-- B
# both a and b are empty because they were pointing
# to the same list whose elements were just removed