Everything about lists
-----------------------

-  Lists are containers, containing items indexed by their location.

-  Location starts at 0 from left and -1 from right. 

   ::
      
      >>> animals
      ['dog', 'cat', 'pig']
      >>> animals[0]
      'dog'
      >>> animals[1]
      'cat'
      >>> animals[2]
      'pig'
      >>> animals[3]
      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
      IndexError: list index out of range
      >>> animals[-1]
      'pig'
      >>> animals[-2]
      'cat'
      >>> animals[-3]
      'dog'
      >>> animals[-4]
      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
      IndexError: list index out of range

-  Valid list indices are between (0, len(L)-1) and (-1, -len(L)).
   
List operations
~~~~~~~~~~~~~~~~

-  These operations do not return anything and alter the list that they
   are applied to (append, insert, remove, sort):

   ::

      >>> animals
      ['dog', 'cat', 'pig']
      >>> animals.append('cow')
      >>> animals
      ['dog', 'cat', 'pig', 'cow']
      >>> animals.insert(2,'bird')
      >>> animals
      ['dog', 'cat', 'bird', 'pig', 'cow']
      >>> animals.remove('cat')
      >>> animals.remove('cat')
      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
      ValueError: list.remove(x): x not in list
      >>> animals
      ['dog', 'bird', 'pig', 'cow']
      >>> animals.sort()
      >>> animals
      ['bird', 'cow', 'dog', 'pig']

-  This operation returns a value from the list and modifies the list:

   ::

      >>> animals
      ['dog', 'cat', 'pig', 'cow']
      >>> animal = animals.pop()
      >>> animals
      ['dog', 'cat', 'pig']
      >>> animal
      'cow'

      
-  These operations return a new list by copying the top level element
   in each list, hence called a shallow copy (+,*,list,sorted,slicing): 

   ::

      >>> birds = ['cardinal','bluebird','sparrow']
      >>> animals = ['dog','cat','pig']
      >>> 
      >>> birds + animals
      ['cardinal', 'bluebird', 'sparrow', 'dog', 'cat', 'pig']
      >>> multibird = birds*2
      >>> multibird
      ['cardinal', 'bluebird', 'sparrow', 'cardinal', 'bluebird', 'sparrow']
      >>> birds_copy = list(birds)
      >>> allanimals = birds + animals
      >>> allanimals.append('hippo')
      >>> someanimals = animals[1:3]
      >>> someanimals
      ['cat', 'pig']
      >>> allanimals
      ['cardinal', 'bluebird', 'sparrow', 'dog', 'cat', 'pig', 'hippo']
      >>> birds
      ['cardinal', 'bluebird', 'sparrow']
      >>> animals
      ['dog', 'cat', 'pig']
      >>> ### see original lists are not changed


-  Slicing produces a new list, by copy and pasting values from the
   original list, L[s:e:i], from starting index s, to ending index e
   and incrementing by i.

   ::

      >>> allanimals
      ['cardinal', 'bluebird', 'sparrow', 'dog', 'cat', 'pig', 'hippo']
      >>> allanimals[1:5:2]
      ['bluebird', 'dog']
      >>> allanimals[-2:-4]
      []
      >>> allanimals[-2:-4:-1]
      ['pig', 'cat']
      >>> allanimals[::-1]
      ['hippo', 'pig', 'cat', 'dog', 'sparrow', 'bluebird', 'cardinal']

      
-  You can apply the same principles to list of lists.

   ::

      >>> names = [ ['Sun', 500], ['Moon', 200] ]
      >>> names[0]
      ['Sun', 500]
      >>> names[0][0]
      'Sun'
      >>> names[0][1]
      500
      >>> names[1]
      ['Moon', 200]
      >>> names[1][-1]
      200
      >>> names[0][:1]
      ['Sun']
      >>> names[0].append(200)
      >>> names
      [['Sun', 500, 200], ['Moon', 200]]


   As this is a list of lists, then the 0th item is a list. You can
   apply the same list functions to this list as well.