Internet & World Wide Web How to Program, 3/e

ISBN: 0-13-145091-3 © 2004 pages: 1420 Order

Python defines several data structures that help programmers store and manipulate data quickly and easily. This tutorial presents Python's built-in data structures for lists (list and tuple) and key-value pairs (dictionary). The tutorial is intended for students and developers who are familiar with basic Python programming, or for people who have read our prior Python articles, Introduction to Python and Python Basic Data Types, Control Statements and Functions.

[Note: This tutorial is an excerpt (Section 35.3) of Chapter 35, Python, from our textbook Internet & World Wide Web How to Program, 3/e. This tutorial may refer to other chapters or sections of the book that are not included here. Permission Information: Deitel, Harvey M. and Paul J., INTERNET & WORLD WIDE WEB HOW TO PROGRAM, 3/E, ©2004, pp.1246-1251. Electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.]

35.3   Tuples, Lists and Dictionaries

In addition to basic data types that store numerical values and strings, Python defines three data types for storing more complex data: the list (a sequence of related data), the tuple (pronounced too-ple; a list whose elements may not be modified) and a dictionary (a list of values that are accessed through their associated keys). These data types are high-level implementations of simple data structures that enable Python programmers to manipulate many types of data quickly and easily. Some Python modules (e.g., Cookie and cgi) use these data types to provide simple access to their underlying data structures. Figure 35.7 is a program that illustrates tuples, lists and dictionaries.

Fig. 35.7 Tuples, lists and dictionaries.

1   # Fig. 35.7: fig35_07.py

2   # A program that illustrates tuples, lists and dictionaries.

3

4   # tuples

5   aTuple = ( 1, "a", 3.0 ) # create tuple

6   firstItem = aTuple[ 0 ] # first tuple item

7   secondItem = aTuple[ 1 ] # second tuple item

8   thirdItem = aTuple[ 2 ] # third tuple item

9

10   print "The first item in the tuple is", firstItem

11   print "The second item in the tuple is", secondItem

12   print "The third item in the tuple is", thirdItem

13   print

14

15   firstItem, secondItem, thirdItem = aTuple

16   print "The first item in the tuple is", firstItem

17   print "The second item in the tuple is", secondItem

18   print "The third item in the tuple is", thirdItem

19   print

20

21   aTuple += ( 4, )

22   print "Used the += statement on the tuple"

23   print

24

25   # print the tuple

26   print "The raw tuple data is:", aTuple

27   print "The items in the tuple are:"

28

29   for item in aTuple: # print each item

30      print item,

31

32   print # end previous line

33   print # blank line

34

35   # lists

36   aList = [ 1, 2, 3 ] # create list

37   aList[ 0 ] = 0 # change first element of list

38   aList.append( 5 ) # add item to end of list

39

40   print "The raw list data is:", aList # print list data

41   print

42

43   aList += [ 4 ] # add an item to the end of the list

44   print "Added an item to the list using the += statement"

45   print

46

47   # print each item in the list

48   print "The items in the list are:"

49

50   for item in aList:

51      print item,

52

53   print # end previous line

54   print # blank line

55

56   # dictionaries

57   aDictionary = { 1 : "January", 2 : "February", 3 : "March",

58                   4 : "April", 5 : "May", 6 : "June", 7 : "July",

59                   8 : "August", 9 : "September", 10 : "October",

60                   11 : "November" }

61   aDictionary[ 12 ] = "December" # add item to dictionary

62

63   print "The raw dictionary data is:", aDictionary

64   print "\nThe entries in the dictionary are:"

65

66   for item in aDictionary.keys():

67      print "aDictionary[ ", item, " ] = ", aDictionary[ item ]

The first item in the tuple is 1 The second item in the tuple is a The third item in the tuple is 3.0 The first item in the tuple is 1 The second item in the tuple is a The third item in the tuple is 3.0 Used the += statement on the tuple The raw tuple data is: (1, 'a', 3.0, 4) The items in the tuple are: 1 a 3.0 4 The raw list data is: [0, 2, 3, 5] Added an item to the list using the += statement The items in the list are: 0 2 3 5 4 The raw dictionary data is: {12: 'December', 11: 'November', 10: 'October', 9: 'September', 8: 'August', 7: 'July', 6: 'June', 5: 'May', 4: 'April', 3: 'March', 2: 'February', 1: 'January'} The entries in the dictionary are: aDictionary[ 12 ] = December aDictionary[ 11 ] = November aDictionary[ 10 ] = October aDictionary[ 9 ] = September aDictionary[ 8 ] = August aDictionary[ 7 ] = July aDictionary[ 6 ] = June aDictionary[ 5 ] = May aDictionary[ 4 ] = April aDictionary[ 3 ] = March aDictionary[ 2 ] = February aDictionary[ 1 ] = January

 

Other Python Tutorials:
Introduction to Python
Pytthon Basic Data Types, Control Statements and Functions
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