A Python 2.7 programming tutorial

All list instances have methods for changing the values in the list. These methods work only on lists. They do not work on the other sequence types that are not mutable, that is, the values they contain may not be changed, added, or deleted.

For example, for any list instance L, the .append(v) method appends a new value v to that list.

>>> menu1 = ['kale', 'tofu']
>>> menu1
['kale', 'tofu']
>>> menu1.append ( 'sardines' )
>>> menu1
['kale', 'tofu', 'sardines']
>>> 

To insert a single new value V into a list L at an arbitrary position P, use this method:

L.insert(P, V)

To continue the example above:

>>> menu1
['kale', 'tofu', 'sardines']
>>> menu1.insert(0, 'beans')
>>> menu1
['beans', 'kale', 'tofu', 'sardines']
>>> menu1[3]
'sardines'
>>> menu1.insert(3, 'trifle')
>>> menu1
['beans', 'kale', 'tofu', 'trifle', 'sardines']

The method L.remove(V) removes the first element of L that equals V, if there is one. If no elements equal V, the method raises a ValueError exception.

>>> menu1
['beans', 'kale', 'spam', 'spam', 'spam', 'tofu', 'trifle', 'sardines']
>>> menu1.remove('spam')
>>> menu1
['beans', 'kale', 'spam', 'spam', 'tofu', 'trifle', 'sardines']
>>> menu1.remove('spam')
>>> menu1
['beans', 'kale', 'spam', 'tofu', 'trifle', 'sardines']
>>> menu1.remove('gravy')
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: list.remove(x): x not in list

The L.sort() method sorts the elements of a list into ascending order.

>>> menu1
['beans', 'kale', 'spam', 'tofu', 'trifle', 'sardines']
>>> menu1.sort()
>>> menu1
['beans', 'kale', 'sardines', 'spam', 'tofu', 'trifle']

Note that the .sort() method itself does not return a value; it sorts the values of the list in place. A similar method is .reverse(), which reverses the elements in place:

>>> menu1
['beans', 'kale', 'sardines', 'spam', 'tofu', 'trifle']
>>> menu1.reverse()
>>> menu1
['trifle', 'tofu', 'spam', 'sardines', 'kale', 'beans']