Introductory Programming
Fall 2004

For Thursday you should:

1) Finish homework 6.

2) If you didn't get a check on Eval 4, work on Eval 4b.

3) Prepare for an evaluation on Chapter 8.

Homework 6 questions?


Lists
-----

A list is like a string except 

1) the elements can be any type of value

2) lists are mutable


Ways to make lists:

1) bracket operators:

   t = [1, 2, 3]

2) range function

   t = range(3)

3) list function

   t = list('allen')


Lists and for loops:

for x in [1, 2, 3]:
    print x


for x in range(3):
    print x


for x in list('allen'):
    print x


Exercises:

1) write a loop that traverses a list of integers and
   counts the number of elements that are even

   now encapsulate it is a function named count_even

2) write a loop that traverses a list of integers and
   prints each element of the list squared.

   encapsulate it in a function named print_squares

3) write a loop that traverses a list of integers and
   adds up the total of all the elements.

   encapsulate it in a function named list_sum


List methods
------------

Many list operations are methods, which are functions that
you invoke on a list using dot notation.

Try this:

t = [1, 2, 3]
t.append(4)
print t

t.reverse()
print t

import random
random.shuffle(t)    # just a plain old function in the random module
print t

t.sort()
print t


append
------

The append method is often used to build a list incrementally.

What does the following function do?

def mystery(t):
    result = []
    for x in t:
	result.append(x**2)
    return result

print mystery(range(4))


Sequences
---------

Sequence operations

http://www.python.org/doc/current/lib/typesseq.html

Mutable sequence operations

http://www.python.org/doc/current/lib/typesseq-mutable.html