Chapter 5 Functions. Dr. Zhang COSC 1436 Summer, 2018 June 19, 2018

Transcription

1 Chapter 5 Functions Dr. Zhang COSC 1436 Summer, 2018 June 19, 2018

2 while Loop Repetition Review A Condition-Controlled Loop Causes a statement or set of statements to repeat as long as a condition is true. It tests its condition before performing an iteration, which is also known as a protest loop. Example: n = 10 # initialize sum and counter sum = 0 i = 1 while i <= n: sum = sum + i i = i+1 # print the sum # update counter print("the sum is", sum)

3 For Loop Repetition Review A count-controlled loop iterates a specific number of times. Example: # Prints out the numbers 0,1,2,3,4 for x in range(5): print(x) # Prints out 3,4,5 for x in range(3, 6): print(x) # Prints out 3,5,7 for x in range(3, 8, 2): print(x)

4 Repetition Review Augmented assignment operators

5 Nested Loop Repetition Review Python programming language allows to use one loop inside another loop you can put any type of loop inside of any other type of loop. For example a for loop can be inside a while loop or vice versa. i = 0 kebab = ["chicken","garlic","cheese","tomato","lettuce","chilli"] print "Kebabs are so good, this is what mine has:" excitement_over_kebab = 1 for ingredients in kebab: while excitement_over_kebab == 1: print kebab[i] i+=1 if i == 6: print "Enough talk, my lunch break is over." excitement_over_kebab = 0

6 Chapter 5: Functions Concept: A function is group of statements that that exist within a program for the purpose of performing a specific task. Example: An overall task of calculating an travel cost would consist of several subtasks, Such as : Getting the air fare Getting the cost of ground transportation Calculating the lodge cost Calculating the meals cost Calculating the other costs Printing the total cost The program performs the task can be broken down into several subtasks. For this reason, we usually break down the programs into small manageable pieces known as functions. This approach is also called divide and conquer

7 Designing a Program to Use Functions Top-Down Design The overall task that the program is to perform is broken down into a series of subtasks. Each of the subtasks is examined to determine whether it can be further broken down into more subtasks. This step is repeated until no more subtasks can be identified. Once all of the subtasks have been identified, they are written in code.

8 Designing a Program to Use Functions Using IPO Charts IPO stands for input, processing, and output. An IPO chart is a simple but effective tool for programmer to use for designing and documenting functions.

9 Benefits of Modularizing a program Simpler Code with functions easy read and manage Code reuse reduce the duplication of code Better testing can test each function individually Faster Development same function can be used by different programs Easier Facilitation of Teamwork

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11 Defining and Calling a Void Function Function Name Roles: python requires that you follow the same rules that you follow when naming variables: Can not use one of Python s key words as a variable name. A function name can not contains space. The first character must be one of the letters a through z, A through Z or under-score character(_) After the first character you may use one of the letters a through z, A through Z, the digit 0 through 9 or under-score character(_) name is case sensitive.

12 Defining and Calling a Void Function Concept: The code for a function is known as a function definition. To execute the function, you write a statement that calls it. ##Defining a function: def function_name(): Statement Statement ##Calling a function: function_name()

13 Defining and Calling a Void Function Code example: # This program demonstrates a function. # First, we define a function named main. def main(): print('i am Arthur') print('king of the Britons') # Call the message function. main()

14 # This program has two functions. First we # define the main function. def main(): print('i have a message for you.') message() print('goodbye!') # Next we define the message function. def message(): print('i am Arthur') print('king of the Britons.') # Call the main function. main() Program Output I have a message for you. I am Arthur King of the Britons Goodbye! Code example

15 Local Variables Concept: A local variable is created inside a function and cannot be accessed by statements that are outside the function. Different functions can have local variables with the same names because the functions cannot see each other s local variables. Scope: A variable s scope is that part of a program in which the variable may be accessed. A variable is visible only to statements in the variable s scope. A local variable s scope is the function in which the variable is created.

16 Local Variables Code example: # This program demonstrates two functions that have local variables with the same name. def main(): texas() # Call the texas function. california() # Call the california function. # Definition of the texas function. def texas(): birds = 5000 # a local variable named birds. print('texas has', birds, 'birds.') # Definition of the california function. def california(): birds = 8000 # a local variable named birds. print('california has', birds, 'birds.') # Call the main function. main()

17 Passing Arguments to Functions Concept: An argument is any piece of data that is passed into a function when the function is called. A parameter is a variable that receives an argument that is passed into a function.

18 Passing Arguments to Functions Code example # This program demonstrates an argument being # passed to a function. def main(): value = 5 show_double(value) ## value is argument # The show_double function accepts an argument # and displays double its value. def show_double(number): ## number is parameter result = number * 2 print(result) # Call the main function. main()

19 Passing Arguments to Functions- Cont Parameter Variable Scope: A parameter variable s scope is the function in which the parameter is used. Passing Multiple Arguments: In Python, functions can accept multiple arguments. # This program demonstrates a function that accepts # two arguments. def main(): print('the sum of 12 and 45 is') show_sum(12, 45) # The show_sum function accepts two arguments and displays their sum. def show_sum(num1, num2): result = num1 + num2 print(result) main() ## Call the main function

20 Passing Arguments to Functions- Cont Code example (passing strings) # This program demonstrates passing two string # arguments to a function. def main(): first_name = input('enter your first name: ') last_name = input('enter your last name: ') print('your name reversed is') reverse_name(first_name, last_name) def reverse_name(first, last): print(last, first) # Call the main function. main()

21 Passing Arguments to Functions- Cont Making Changes to Parameters. You can change the value of the parameters. # This program demonstrates what happens when you change the value of a parameter. def main(): value = 99 print('the value is', value) change_me(value) print('back in main the value is', value) def change_me(arg): print('i am changing the value.') arg = 0 print('now the value is', arg) main() # Call the main function.

22 Passing Arguments to Functions- Cont Keyword Arguments The Python language allows you to write an argument in the following format to specify which parameter variable the argument should be passed to: Parameter_name=value (syntax) Example: def main(): show_interest(rate=0.01, periods=10, principal=1000.0) def show_interest(principle, rate, periods): interest = principal * rate * periods print( The simple interest will be $, format(interest,,.2f ), sep= ) # call the main function main()

23 Global Variables and Global Constants global variable : A global variable is accessible to all the functions in a program file. The keyword global is only useful to change or create global variables in a local context, although creating global variables is seldom considered a good solution. 1. # Create a global variable. my_value = 10 # The show_value function prints # the value of the global variable. def show_value(): print(my_value) # Call the show_value function. show_value()

24 Global Variables and Global Constants global variable : A variable can't be both local and global inside of a function. So Python decides that we want a local variable due to the assignment to s inside of f(), so the first print statement before the definition of s throws the error message above. Any variable which is changed or created inside of a function is local, if it hasn't been declared as a global variable. To tell Python, that we want to use the global variable, we have to explicitly state this by using the keyword "global", as can be seen in the following example: def f(): global s ## keyword global print(s) s = "Only in spring, but London is great as well!" print(s) s = "I am looking for a course in Paris!" # a f() print(s)

25 Global Variables and Global Constants Concept: A global constant is a global name that references a value that can not be changed. # The following is used as a global constant to represent the contribution rate. CONTRIBUTION_RATE = 0.05 def main(): gross_pay = float(input('enter the gross pay: ')) bonus = float(input('enter the amount of bonuses: ')) show_pay_contrib(gross_pay) show_bonus_contrib(bonus). def show_pay_contrib(gross): #Calculate the retirement contribution contrib = gross * CONTRIBUTION_RATE print('contribution for gross pay: $', format(contrib, ',.2f'), sep='') def show_bonus_contrib(bonus): #calculate the contrib = bonus * CONTRIBUTION_RATE print('contribution for bonuses: $', format(contrib, ',.2f'), sep='') main() # Call the main function.

26 Concept: Introduction to Value-Returning Functions: 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. A value-returning function is a special type of function. It is like a void function in the following ways. It is a group of statements that perform a specific task When you want to execute the function, you call it

27 Introduction to Value-Returning Functions: Standard Library Functions and the import statement import math This statement causes the interpreter to load the contents of the math module into memory and makes all the functions in the math module available to the program Import random This statement causes the interpreter to load the contents of the random module into memory and makes all the functions in the random module available to the program

28 Introduction to Value-Returning Functions: Generating Random Numbers Import random Functions: random.randint(1,10) #generate random integer random.randrange(0,101,10) There is one slight difference when used with just two parameters. randint(x,y) will return a value >= x and <= y, while randrange(x,y) will return a value >=x and < y (n.b. not less than or equal to y) There is a bigger difference if you use the additional parameter that randrange can take... randrange(start, stop, step)

29 Introduction to Value-Returning Functions: Generating Random Numbers Import random Functions: random.random random.uniform(1.0,10.0) random.random() gives you a random floating point number in the range [0.0, 1.0) (so including 0.0, but not including 1.0). random.uniform(a, b) gives you a random floating point number in the range [a, b], (where rounding may end up giving you b).

30 Introduction to Value-Returning Functions: # This program displays a random number in the range of 1 through 10. import random def main(): number = random.randint(1, 10) # Get a random number. print('the number is', number) # Display the number. # Call the main function. main()

31 Introduction to Value-Returning Functions: # This program displays five random # numbers in the range of 1 through 100. import random def main(): for count in range(5): # Get a random number. number = random.randint(1, 100) # Display the number. print(number) # Call the main function. main()

32 Introduction to Value-Returning Functions: # This program simulates 10 tosses of a coin import random # GLOBAL Constants HEADS = 1 TAILS = 2 TOSSES = 10 def main(): for toss in range(tosses): # Simulate the coin toss. if random.randint(heads, TAILS) == HEADS: print('heads') else: print('tails') main() # Call the main function.

33 Introduction to Value-Returning Functions: randrange, random, seed, and uniform Functions number = random.randrange(10) number=random.randrange(5,10) number=random.randrange(0,101,10) number=random.uniform(1.0,10.0) Random.seed(10) import random random.seed( 3 ) Print( "Random number with seed 3 : ", random.random() ) #will generate a random number #if you want to use the same #random number once again in your #program random.seed( 3 ) random.random() # same random number as before

34 Introduction to Value-Returning Functions: Concept: The Python standard library s math module contains numerous functions that can be used in mathematical calculations Example: result = math.sqrt(16), mypi=math.pi, mye=math.e

35 Writing Your Own Value-Returning Function Concept: A value-returning function has a return statement that returns a value back to the part of the program that called it. Sytanx: def function_name(): Statement Statement Etc. Return expression

36 Writing Your Own Value-Returning Function Example: # This program uses the return value of a function. def main(): first_age = int(input('enter your age: ')) # Get the user's age. second_age = int(input("enter your best friend's age: ")) total = sum(first_age, second_age) # Display the total age. print('together you are', total, 'years old.') # The sum function accepts two numeric arguments and returns the sum of those arguments. def sum(num1, num2): result = num1 + num2 return result main() # Call the main function.

37 Writing Your Own Value-Returning Function Return string, Boolean values, multiple values Code example: def get_name(): name=input( Enter your name: ) return name def is_even(number): if number = 1 status = True else status = false return status

38 Writing Your Own Value-Returning Function Return string, Boolean values, multiple values Code example: def get_fullname(): firstname = input( Enter your first name ) lastname = input( Enter your last name ) #return both name return firstname, lastname # call get_fullname function first_name, last_name = get_fullname()

39 Writing Your Own Value-Returning Function EXAMPLE: Text book: page 211

40 Lab exercise and Assignment Lab : Chapter 5: Programming Exercises: 1,3,5,8,13 Due 6/21/2018 ( show your code to me in class) Review questions. Assignments: Chapter 5: Programming Exercises : 14, 19,20,21 Due 6/26/2018 ( show your code to me in class)