Lists

• lists are “collections of things” which have a particular order

• you can add and remove items to the list (unlike tuples)

• lists can contain any type of object, including other lists

>>> integers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> integers
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> integers.append( 11 )
>>> integers
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11]
>>> integers.insert( 0, 12 )
>>> integers
[12, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11]
>>> len(integers)
12
>>> sorted(integers)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12]
>>> integers # why didn't integers change?
[12, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11]
>>> integers.sort()
>>> integers # the .sort() method did an "in place" sort
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12]
>>> integers.append( 'apple' )
>>> integers
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 'apple']

>>> lists = [ [1,2],[3,4],[5,6]]
>>> lists
[[1, 2], [3, 4], [5, 6]]
>>> lists[0]
[1, 2]

Note

What did integers.append( 11 ) mean?

Here the object integers had a piece of code attached to it (we call these “methods”) which was written to “add an object to the end of THIS list”. By writing integers.append we “looked up” this piece of code in the integers list. When we added the ( 11 ) to the statement we asked that piece of code (append) to act on a single integer object 11 within the context of the list object.

Note

Python’s interactive interpreter has a help function that allows you to get documentation on a particular type of object, such as list. The help text normally includes all of the “methods” that are available, a description of the parameters for each method, and normally a “docstring” (human description) for the method explaining what it does, and occasionally how it does it.

>>> help( list ) # type <q> to exit the help

Tuples

Tuples are pretty-much like lists, except that you can’t change them after you create them:

>>> integers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
>>> integers
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
>>> len(integers)
10
>>> integers.append
Traceback (most recent call last):
  File "/usr/lib/python2.7/doctest.py", line 1315, in __run
    compileflags, 1) in test.globs
  File "<doctest default[3]>", line 1, in <module>
    integers.append
AttributeError: 'tuple' object has no attribute 'append'

We normally don’t use tuples like this, we normally use tuples as a way to pack together things in a “lightweight structure” or “object”. So if you want to represent a pair of coordinates (x,y) you might use a tuple of floating-point values.

>>> direction = (1,1)
>>> x,y = direction
>>> direction = (x+1,y-2)
>>> direction
(2, -1)

List Indexing shows you how to work with the items inside a list (or tuple).