This document provides an introduction to using lists in Python. It defines what lists are in Python, how to create, access, update, and delete list elements, and some common list operations. It also provides examples of creating lists, accessing values at different indices, updating and deleting elements, and using basic operators like addition and multiplication. Finally, it proposes three exercises involving lists to practice these concepts.

1. Introduction to
Programming with
Python – Class 4
SYED FARJAD ZIA ZAIDI

2. Class Objectives
Class Objective
Understanding Lists
Write few simple programs that use lists.

3. Class Material
•Chapter 6, 8 -
Python for
Informatics:
Exploring
Information
Reading

4. Lists
 The most basic data structure in Python is the sequence.
Each element of a sequence is assigned a number - its
position or index. The first index is zero, the second index
is one, and so forth.
 Python has six built-in types of sequences, but the most
common ones are lists and tuples, which we would see
in this tutorial.
 There are certain things you can do with all sequence
types. These operations include indexing, slicing, adding,
multiplying, and checking for membership. In addition,
Python has built-in functions for finding the length of a
sequence and for finding its largest and smallest
elements.

5. Creating Lists
 Creating a list is as simple as putting different comma-separated
values between squere brackets. For example:
list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5 ];
list3 = ["a", "b", "c", "d"];

6. Accessing Values in Lists:
 To access values in lists, use the square brackets for slicing along
with the index or indices to obtain value available at that index.
Following is a simple example:
list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5, 6, 7 ];
print "list1[0]: ", list1[0]
print "list2[1:5]: ", list2[1:5]

7. Updating Lists
 You can update single or multiple elements of lists by giving the slice
on the left-hand side of the assignment operator, and you can add
to elements in a list with the append() method. Following is a simple
example:
list = ['physics', 'chemistry', 1997, 2000];
print "Value available at index 2 : "
print list[2];
list[2] = 2001;
print "New value available at index 2 : "
print list[2];

8. Delete Lists Elements
 To remove a list element, you can use either the del statement if you
know exactly which element(s) you are deleting or the remove()
method if you do not know. Following is a simple example:
list1 = ['physics', 'chemistry', 1997, 2000];
print list1;
del list1[2];
print "After deleting value at index 2 : "
print list1;

9. Basic List Operations
 Lists respond to the + and * operators much like strings; they mean
concatenation and repetition here too, except that the result is a
new list, not a string.
 In fact, lists respond to all of the general sequence operations we
used on strings in the prior chapter.

10. List Operations
Python Expression Results Description
len([1, 2, 3]) 3 Length
[1, 2, 3] + [4, 5, 6] [1, 2, 3, 4, 5, 6] Concatenation
['Hi!'] * 4 ['Hi!', 'Hi!', 'Hi!', 'Hi!'] Repetition
3 in [1, 2, 3] True Membership
for x in [1, 2, 3]: print x, 1 2 3 Iteration

11. Exercise 0
 Create a program that will keep track of items for a shopping list.
The program should keep asking for new items until nothing is
entered (no input followed by enter/return key). The program should
then display the full shopping list.

12. Exercise 1
 Given an array of ints, return True if 6 appears as either the first or last
element in the array. The array will be length 1 or more.
first_last6([1, 2, 6]) → True
first_last6([6, 1, 2, 3]) → True
first_last6([13, 6, 1, 2, 3]) → False

13. Exercise 2
 Given an array of ints, return True if the array is length 1 or more, and
the first element and the last element are equal.
same_first_last([1, 2, 3]) → False
same_first_last([1, 2, 3, 1]) → True
same_first_last([1, 2, 1]) → True

14. Exercise 3
 Return the number of even ints in the given array. Note: the % "mod"
operator computes the remainder, e.g. 5 % 2 is 1.
count_evens([2, 1, 2, 3, 4]) → 3
count_evens([2, 2, 0]) → 3
count_evens([1, 3, 5]) → 0

15. Any Queries?
 Link to Facebook Group:
https://www.facebook.com/groups/introtopython.iccbs/
 Email:
farjad_bullet@rocketmail.com