"""Exploring lists as mutable objects
http://openbookproject.net/thinkcs/python/english2e/ch09.html#lists-are-mutable
"""

a = "banana"
b = "banana"

# do a and b point to the same object in memory?

id(a)
id(b)

# Python only created one string, and both a and b refer to it. 

# lists behave differently. When we create two lists, we get two objects:

a = [1, 2, 3]
b = [1, 2, 3]

id(a)
id(b)

# Since variables refer to objects, if we assign one variable to another, 
# both variables refer to the same object:

a = [1, 2, 3]
b = a
id(a) == id(b)

# if we change b, that also changes a
b[0] = 5
print a

# If we want to modify a list and also keep a copy of the original, we need 
# to be able to make a copy of the list itself, not just the reference. 
# This process is sometimes called cloning, to avoid the ambiguity of the word copy.

# The easiest way to clone a list is to use the slice operator:

a = [1, 2, 3]
b = a[:]
print b
a == b
id(a) == id(b)

# the equality operator for lists determines if all elements of the two lists are the same

# Now we are free to make changes to b without worrying about a:
b[0] = 5
print a