Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley STARTING OUT WITH Python Python First Edition by Tony Gaddis Chapter 6 Value-Returning Functions and Modules

1-2 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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.

1-3 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Introduction to Value-Returning Functions: Generating Random Numbers 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

1-4 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Introduction to Value-Returning Functions: Generating Random Numbers 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()

1-5 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Introduction to Value-Returning Functions: Generating Random Numbers Figure 6-1 The age variable references the value 25

1-6 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Introduction to Value-Returning Functions: Generating Random Numbers 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

1-7 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Introduction to Value-Returning Functions: Generating Random Numbers Program 6-2 (random_numbers2.py)

1-8 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Introduction to Value-Returning Functions: Generating Random Numbers # generates a random integer number in the range of 5 through 9 number = 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 1.0 number = random.random() # generates a random floating-point number in the range of 1.0 through 10.0 number = random.uniform(1.0, 10.0)

1-9 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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 3-9

1-10 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Random Decimal (Floating Point) Numbers random() random decimal numbers 0.0 through 1.0: uniform(1.0,10.0) random decimal numbers 1.0, through 10.0:

1-11 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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.

1-12 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions def function_name(): statement etc. return expression Figure 6-5 Parts of the function

1-13 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions Program 6-6 (total_ages.py)

1-14 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions Making the Most of the return statement def sum(num1, num2): result = num1 + num2 return result def sum(num1, num2): return num1 + num2

1-15 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions 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

1-16 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions Figure 6-7 IPO charts for the getRegularPrice and discount functions

1-17 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions Returning Strings def get_name(): # Get the user’s name name = raw_input(‘Enter your name:’) # Return the name return name

1-18 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions 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 = True else: status = False return status def is_even(number): if (number % 2) == 0: status = True else: status = False return status For example: Determine whether a number is even or odd … For example: Validate user input…

1-19 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Writing Your Own Value-Returning Functions 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

1-20 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley The math Module Concept: The Python standard library’s math module contains numerous functions that can be used in mathematical calculations.

1-21 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley The math Module Table 6-2 Many of the functions in the math module

1-22 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley The math Module Program 6-9 (square_root.py)

1-23 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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.

1-24 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Storing Functions In Modules 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

1-25 Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Storing Functions In Modules 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

Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley QUESTIONS ? Chapter 6 Value-Returning Functions and Modules