Passing Arguments, Local/Global Variables Writing Functions( ) (Part 2)

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >>

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning Welcome to class

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning Welcome to class

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning Welcome to class

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning Welcome to class Hi, there!

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning Welcome to class Hi, there! I’m a function.

def hello( ): print (“Hi, there!”) print (“I’m a function.”) print (“Good morning”) print (“Welcome to class”) hello( ) print (“And, now we’re done”) Flow of Execution >> Good morning Welcome to class Hi, there! I’m a function. And, now we’re done

def hello( ): print (“hey there!”) def goodbye( ): print (“see you later!”) print (“hi!”) hello( ) print (“I’ll see you again”) goodbye( ) Multiple Functions

def hello( ): print (“hey there!”) def goodbye( ): print (“see you later!”) print (“hi!”) hello( ) print (“I’ll see you again”) goodbye( ) Multiple Functions >> hi! hey there! I’ll see you again see you later!

def main( ): print (“I have a message!”) message( ) print (“Goodbye!”) def message( ): print (“The answer is C!”) print (“Here we go” ) main( ) Functions within a Function

def main( ): print (“I have a message!”) message( ) print (“Goodbye!”) def message( ): print (“The answer is C!”) print (“Here we go” ) main( ) Functions within a Function >> Here we go I have a message! The answer is C! Goodbye!

Functions are like “mini programs” You can create variables inside functions, as you would in your main source code Local Variables

def rectangle( ): x = float(input(“length?: ”)) #local variable y = float(input(“width?: ”)) #local variable area = x * y #local variable print (“Area: ”, area) rectangle( ) Local Variables

However, variables that are defined inside of a function, they are considered “local” to that function Therefore, these local variables cannot be accessed from outside the function’s “scope”, because they simple do not exist to the main program Local Variables

def rectangle( ): x = float(input(“length?: ”)) #local variable y = float(input(“width?: ”)) #local variable area = x * y #local variable print (“Area: ”, area) print( x * y ) # error, x and y are not defined Local Variables

Because local variables don’t “exist” outside the scope of the function, different functions can use the same name for variables defined in their function These local variables, although carrying the same name, do not overwrite one another Local Variables

def Donald( ): money = 3000#local variable print (“Donald has $”, money) def Johnson( ): money = 4000#local variable print (“Johnson has $”, money) Local Variables

Functions can also take arguments, some more than others, as we’ve seen already print(“hello”, “goodbye”, 75) # 3 arguments format(“hello”, “<20s”) # 2 arguments input(“length?: ”) # 1 argument Arguments are separated by commas Passing Arguments to a Function

We can define functions that pass an argument We need to specify what exactly we are going to pass into the function, and what to do with it. We can do this by the use of variables. Passing Arguments to a Function

def square(side): # whatever is passed into print(side ** 2) # the square( ) function # will assume the value # of the variable “side” square(5) # variable “side” is assuming value 5 >> 25 Local Variables

You can define a function that passes multiple arguments Each argument is separated by a comma Each argument is assigned to the variable in the position in which it is defined in the function Passing Multiple Arguments

def average (test1, test2, test3): sum = test1 + test2 + test3 avg = sum / 3 print(avg) #test1 assumes 95 #test2 assumes 98 average(95, 98, 88) #test3 assumes 88 >> Local Variables

When arguments are passed into a function, we are actually passing the “value” into the function, not the actual variable Rules for Arguments

def change (num): print(“original value:”, num) num = 16 print(“new value: “, num) num = 5 change(num) print(“value:”, num) Local Variables

def change (num): print(“original value:”, num) num = 16 print(“new value: “, num) num = 5>> original value: 5 change(num) new value: 16 print(“value:”, num) value: 5 Local Variables

We call this a “passing by value” It creates a one-way communication with the function, meaning we can send data into a function but the function cannot change the argument or communicate back to the main program (We will learn how to create a two-way communication street later) Rules for Arguments

As we discussed, most functions pass arguments by position def function (a, b, c): print(a, b, c) function(1, 2, 3) # variable a holds 1 # variable b holds 2 # variable c holds 3 Keyword Arguments

However, we can also pass arguments by assigning them keywords, or their variable names as defined in the function def function (a, b, c): print(a, b, c) function(b = 1, a = 2, c = 3) Keyword Arguments

You can also pass arguments both by position and with keywords However, you need to pass positional arguments first, then by the keywords Keyword Arguments

def function (a, b, c): print(a, b, c) function( 5, c = 2, b = 3) # here, a holds 5 # b holds 3 # and c holds 2 Keyword Arguments

We said that variables defined inside a function are called “local variables” When variables are created outside of a function, they are called “global variables” We’ve created these global variables all along Global variables can be accessed anywhere in the code, even from inside a function Global Variables

name = “Donald” def sayhello( ): print (“Hey there,”, name) print (“You are”, name) sayhello( ) Global Variables

You can change global variables inside of a function But you must first tell Python you want to do so by adding the keyword “global” before defining the variable inside your function Global Variables

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >>

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >>

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald Hey there, Donald

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald Hey there, Donald

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald Hey there, Donald Hey there, Bryan

name = “Donald” def sayhello( ): global name print (“Hey there,”, name) name = “Bryan” print (“Hey there,”, name) print (“You are”, name) sayhello( ) print (“You are”, name) Global Variables >> You are Donald Hey there, Donald Hey there, Bryan You are Bryan

You can also pass arguments that are inputted by the user into a function def sayhello(name): print( “Hello”, name ) sayhello( input (“What’s your name: ”) ) Global Variables

def square(x): print(“The square of”, x, “is”, x**2) square( int ( input (“Give me a number: ”) ) ) >> Give me a number: 8 The square of 8 is 64 Global Variables

Write a program that defines three functions. One that finds the circumference of a circle, the area of a circle and the volume of a sphere. Then a main program that passes a single variable, which is the radius, into three subsequent functions. Set a global variable for pi and use it in your functions. Practice - Rectangles