STARTING OUT WITH Python First Edition by Tony Gaddis

1. Chapter 6Value-Returning Functions and Modules STARTING OUT WITH PythonFirst Edition by Tony Gaddis

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.

3. 6.1 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

4. 6.1 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()

5. 6.1 Introduction to Value-Returning Functions: Generating Random Numbers Figure 6-1 The age variable references the value 25

6. 6.1 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

7. 6.1 Introduction to Value-Returning Functions: Generating Random Numbers Program 6-2 (random_numbers2.py)

8. 6.1 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)

9. 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

10. 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

11. 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.

12. 6.2 Writing Your Own Value-Returning Functions • def function_name(): • statement • statement • etc. • return expression Figure 6-5 Parts of the function

13. 6.2 Writing Your Own Value-Returning Functions Program 6-6 (total_ages.py)

14. 6.2 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

15. 6.2 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

16. 6.2 Writing Your Own Value-Returning Functions Figure 6-7 IPO charts for the getRegularPrice and discount functions

17. 6.2 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

18. 6.2 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.’ • For example: Determine whether a number is even or odd … • def is_even(number): • if (number % 2) == 0: • status = True • else: • status = False • return status • For example: Validate user input…

19. 6.2 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

20. 6.3 The math Module Concept: The Python standard library’s math module contains numerous functions that can be used in mathematical calculations.

21. 6.3 The math Module Table 6-2 Many of the functions in the math module

22. 6.3 The math Module Program 6-9 (square_root.py)

23. 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.

24. 6.4 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

25. 6.4 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

26. Chapter 6Value-Returning Functions and Modules QUESTIONS ?