and in Python:

>>> True and True
True
>>> True and False
False
>>> False and True
False
>>> False and False
False

Lists

Making a new empty list.

>>> x = []

Let's add some items.

>>> x.append("cows")
>>> x
['cows']
>>> x.append("sheep")
>>> x
['cows', 'sheep']
>>> x.append(42)
>>> x
['cows', 'sheep', 42]

Lists are heterogeneous. They can even contain other lists.

>>> x.append([1,2,3,4])
>>> x
['cows', 'sheep', 42, [1, 2, 3, 4]]

Now we play some indexing games.

>>> x[0]
'cows'
>>> x[3].append(["cats", "dawgs", "elliefants"])
>>> x
['cows', 'sheep', 42, [1, 2, 3, 4, ['cats', 'dawgs', 'elliefants']]]
>>> x[0]
'cows'
>>> x[0][0]
'c'
>>> x[3]
[1, 2, 3, 4, ['cats', 'dawgs', 'elliefants']]
>>> x[3][4]
['cats', 'dawgs', 'elliefants']
>>> x[3][4][2]
'elliefants'
>>> x[3][4][2][0]
'e'

Casting a string to a list explodes it into a list of characters.

>>> list("trinitrotolulene")
['t', 'r', 'i', 'n', 'i', 't', 'r', 'o', 't', 'o', 'l', 'u', 'l', 'e', 'n', 'e']

Humpty Dumpty can be glued back together again. Notice that join was called on a string. It's a string method that takes a list as an argument.

>>> smithereens = list("trinitrotolulene")
>>> "".join(smithereens)
'trinitrotolulene'

Let's go shoppping!


>>> shopping = []
>>> shopping.append("steak")
>>> shopping.append("broccoli")
>>> shopping.append("chocolate milk")
>>> shopping
['steak', 'broccoli', 'chocolate milk']


The len function tells you the number of items
in a list, as well as the length of a string.


>>> len(shopping)
3


The in keyword checks for membership.


>>> "milk" in shopping
False
>>> shopping.append("milk")


Note how in works on strings.


>>> "cow" in "cowabunga"
True


Mutability It's convenient and dangerous.  All of the
scalar types, int, string and boolean are immutable objects. Once created
in memory, they cannot be changed.

Lists are different. They aer mutable.  The state of a list is the 
objects in it and their association to the indices (order).

You are about to see  a mutability pitfall, aliasing.


>>> x = [1,2,3]
>>> y = x
>>> y
[1, 2, 3]
>>> x
[1, 2, 3]
>>> y[0] = 5
>>> y
[5, 2, 3]
>>> x
[5, 2, 3]


Notice that every Python object has an ID, which is its memory
address.


>>> id(x)
140363846671296
>>> id(y)
140363846671296
>>> id(0)
4462098752
>>> id(1)
4462098784
>>> id(2)
4462098816
>>> id(3)
4462098848
>>> id(5)
4462098912
>>> id(100) - id(0)
3200
>>> id(200) - id(0)
6400
>>> id(300) - id(0)
140359387297968
>>>