STARTING OUT WITH Python First Edition by Tony Gaddis

Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

STARTING OUT WITH

PythonPythonFirst Edition

by Tony Gaddis

Chapter 6Value-Returning Functions and Modules

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Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 6-2

6.1 Introduction to Value-Returning Functions: Generating Random Numbers

Concept:

A value-returning function is a function that returns a value back to the part of the program that called it. Python, as well as most other programming languages, provides a library of prewritten functions that perform commonly needed tasks. These libraries typically contain a function that generates random numbers.

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Value-returning function:

•A group of statements that performs a specific task

•Executed when called

•Returns a value back to the part of the program that called it

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Standard Library Functions•Already written and come with the language•Make a programmer’s job easier•Perform many commonly needed tasks•Stored in files known as modules•Include the import statement at the top of the program

For example: input() raw_input() range()

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Figure 6-1 The age variable references the value 25

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Generating Random Numbers

For example:

# causes the interpreter to load the contents of the random module

import random# causes the interpreter to load the contents of

number = random.randint(1, 100)

Figure 6-2 A statement that calls the random function

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Program 6-2 (random_numbers2.py)

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# generates a random integer number in the range of 5 through 9number = random.randrange(5, 10)

# generates a random number in the [0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100]number = random.randrange(0, 101, 10)

# generates a random floating-point number in the range of 0.0 through 1.0number = random.random()

# generates a random floating-point number in the range of 1.0 through 10.0number = random.uniform(1.0, 10.0)

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Random Integers

randint(start,end)

random integers start through end inclusive

randrange(end)

random integers 0 through end-1

randrange(start,end)

random integers start through end -1

randrange(start,end,step)

random integers start, start+step… Up to end

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Random Decimal (Floating Point) Numbers

random()

random decimal numbers 0.0 through 1.0:

0.0863786658417

uniform(1.0,10.0)

random decimal numbers 1.0, through 10.0:

5.97946536804

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6.2 Writing Your Own Value-Returning Functions

Concept:

A value-returning function has a return statement that returns value back to the part of the program that called it.

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def function_name():

statement

statementetc.return

expressionFigure 6-5 Parts of the function

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Program 6-6 (total_ages.py)

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Making the Most of the return statement

def sum(num1, num2):result = num1 +

num2return result

def sum(num1, num2):return num1 + num2

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Using IPO Charts

•A tool used for designing and documenting functions

•IPO stands for Input, Processing, and Output

•Describes the input, processing, and output of a function

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Figure 6-7 IPO charts for the getRegularPrice and discount functions

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Returning Strings

def get_name():

# Get the user’s name

name = raw_input(‘Enter your name:’)

# Return the name

return name

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Returning Boolean Values

number = input(‘Enter a number: ‘)if is_even(number):

print ‘The number is even.’else:

print ‘The number is odd.’

def is_even(number):if (number % 2) == 0:

status = Trueelse:

status = False return status

def is_even(number):if (number % 2) == 0:

status = Trueelse:

status = False return status

For example: Determine whether a number is even or odd …

For example: Validate user input…

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Returning Multiple Values

first_name, last_name =get_name()

def get_name():

# Get the user’s first and last name.first = raw_input(‘Enter your first name: ‘)

last = raw_input(‘Enter your last name: ‘)

# Return both names. return first, last

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6.3 The math Module

Concept:

The Python standard library’s math module contains numerous functions that can be used in mathematical calculations.

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6.3 The math Module

Table 6-2 Many of the functions in the math module

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6.3 The math Module

Program 6-9 (square_root.py)

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6.4 Storing Functions In Modules

Concept:

A module is a file that contains Python code. Large programs are easier to debug and maintain when they are divided into modules.

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• A module is a file that contains Python code

• Modularization makes large programs easier to understand, test, and maintain.

• Each module should contain functions

• Modules make it easier to reuse the same code

• Module file names should end in .py

• A module name cannot be the same as a Python key word

• Place the module in the same folder as the program

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Menu Driven Programs

• Display a list of the operations

• Allow the user to select the operation

• List of operations = menu

• An if-elif-else statement carries out the user’s selection


QUESTIONS

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Chapter 6Value-Returning Functions and Modules

STARTING OUT WITH Python First Edition by Tony Gaddis

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