Introductory Topics on Functions
Introductory Topics on Functions
The Return Type of a Function
Introduction
As is the case for a variable, a function has a type. The type of a function is the type of value the function must produce. Because Python is an inferred language, and it means that the compiler is equipped to figure out the type of value that a function is supposed to produce, you don't have to provide that information. Still you can if you want.
To indicate the type of value that a function is supposed to produce, after the closing parentheses of the function, type -> and the return type.
Practical Learning: Starting a Project
def identify_employee():
fname : str = ""
lname : str = ""
print("Employee Identification")
fname = input("First Name: ")
lname = input("Last Name: ")
return fname + " " + lname
def get_gross_salary():
sal : float = 0.00
sal = float(input("Gross Salary: "))
return salReturning a Known Type
If you want to indicate the type of value that a function produces, after its -> symbol, write that type.
Practical Learning: Starting a Project
def identify_employee() -> str: fname : str = "" lname : str = "" print("Employee Identification") fname = input("First Name: ") lname = input("Last Name: ") return fname + " " + lname def get_gross_salary() -> float: sal : float = 0.00 sal = float(input("Gross Salary: ")) return sal
def identify_employee() -> str:
fname : str = ""
lname : str = ""
print("Employee Identification")
fname = input("First Name: ")
lname = input("Last Name: ")
return fname + " " + lname
def get_gross_salary() -> float:
sal : float = 0.00
sal = float(input("Gross Salary: "))
return sal
def evaluate_tax():
print("============================================")
print("\t - Idaho - State Income Tax -")
print("============================================")
added_amount : float
tax_rate : float
gross_salary : float
print("Enter the information for tax preparation")
employee : str = identify_employee()
gross_salary : float = get_gross_salary()
if gross_salary >= 11_760:
tax_rate = 6.925
added_amount = 543.90
if gross_salary < 11_760:
tax_rate = 6.625
added_amount = 284.20
if gross_salary < 7_840:
tax_rate = 5.625
added_amount = 196.00
if gross_salary < 6_272:
tax_rate = 4.625
added_amount = 123.48
if gross_salary < 4_704:
tax_rate = 3.625
added_amount = 66.64
if gross_salary < 3_136:
tax_rate = 3.125
added_amount = 17.64
if gross_salary < 1_568:
tax_rate = 1.125
added_amount = 0
tax_amount = added_amount + (gross_salary * tax_rate / 100.00)
net_pay = gross_salary - tax_amount
present(employee, gross_salary, tax_rate, added_amount, tax_amount, net_pay)
def present(staff, gross_salary, tax_rate, added_amount, tax_amount, net_pay):
print("============================================")
print("\t- Idaho - State Income Tax -")
print("============================================")
print("Employee Information")
print(f"Employee Name: {staff}")
print("============================================")
print("Tax Information")
print("--------------------------------------------")
print(f"Gross Salary: {gross_salary:7.2f}")
print(f"Tax Rate: {tax_rate}%")
print(f"Amount Added: {added_amount:7.2f}")
print(f"Tax Amount: {tax_amount:7.2f}")
print(f"Net Pay: {net_pay:7.2f}")
evaluate_tax()
print("===========================================")============================================
- Idaho - State Income Tax -
============================================
Enter the information for tax preparation
Employee Identification
First Name: Lucinda
Last Name: Matthews
Gross Salary: 2258.97
============================================
- Idaho - State Income Tax -
============================================
Employee Information
Employee Name: Lucinda Matthews
============================================
Tax Information
--------------------------------------------
Gross Salary: 2258.97
Tax Rate: 3.125%
Amount Added: 17.64
Tax Amount: 88.23
Net Pay: 2170.74
===========================================
Press any key to continue . . .============================================
- Idaho - State Income Tax -
============================================
Enter the information for tax preparation
Employee Identification
First Name: Matthew
Last Name: Robertson
Gross Salary: 6412.46
============================================
- Idaho - State Income Tax -
============================================
Employee Information
Employee Name: Matthew Robertson
============================================
Tax Information
--------------------------------------------
Gross Salary: 6412.46
Tax Rate: 5.625%
Amount Added: 196.00
Tax Amount: 556.70
Net Pay: 5855.76
===========================================
Press any key to continue . . .Named Arguments
Introduction
We already know that you can create a function that takes one parameter, and we know how to call such a function. Here is an example we saw already:
def send_message(msg):
print(msg)
send_message("Please remember to submit your time sheet.")
As an option, to be more precise when calling a function and passing an argument, provide the name of the parameter and assign the desired value to it. Here is an example:
def send_message(msg):
print(msg)
send_message(msg = "Please remember to submit your time sheet.")
In the same way, if you have a function that uses more than one parameter, when calling the function, you can type the name of each parameter and assign the desired value to it. Here is an example:
def describe(name, price):
print("Item Name: ", name)
print("Marked Price: ", price)
print("Fun Department Store")
print("-----------------------------------------------------------")
describe(name = "Men's Alpha Tapered-Fit Stretch Chino Pants", price = 74.95)
print("===========================================================")
One of the wonderful characteristics about this feature is that you can pass the arguments in any order as long as you provide a name for each argument.
Requiring a Named Argument
By default, you have the option of naming or not naming an argument when calling a function. If you want to require that, every time the function is called, the name of a parameter must be specified, pass the first argument as * followed by a comma. As a result, the following code will produce an error:
def send_message(*, msg): print(msg) send_message("Please remember to submit your time sheet.") print("===========================================")
Of course, to solve the problem, you must name the argument when calling the function. In the same way, if you want all arguments of a function to be named when calling a function, start their section with * and a comma. Here is an example:
def send_message(*, year, makeModel, value): print("Vehicle: ", year, makeModel) print("Market Value: ", value) send_message(makeModel="Chevrolet Equinox", value=25800, year=2022) print("===========================================")
This would produce:
Vehicle: 2022 Chevrolet Equinox Market Value: 25800 =========================================== Press any key to continue . . .
If you want to require names for some arguments and not for other arguments, in the parentheses of the function you are creating, type *,. On the left side of *,, put the parameter(s) whose name(s) will not be required. On the right side of *,, put the parameters whose names will be required. When calling the function, the values of the unnamed arguments must be given in the exact order their parameters appear in the function. The other arguments, that must be named, can appear in any order. Here is an example:
def send_message(gasCity, color, gasHighway, *, year, makeModel, value): print("Vehicle: ", year, makeModel) print("MPG City/Highway: ", gasCity, "/", gasHighway) print("Market Value: ", value) send_message(26, "Blue", 31, makeModel="Chevrolet Equinox", value=25800, year=2022) print("===========================================")
This would produce:
Vehicle: 2022 Chevrolet Equinox MPG City/Highway: 26 / 31 Market Value: 25800 =========================================== Press any key to continue . . .
Naming the Arguments
Earlier, we saw that, if you create a function that uses many parameters, when calling the function, you must pass the arguments in the appropriate order. If you pass the arguments in the wrong order, you will receive an error.
To pass the arguments in the order of your choice, you can use the names that were given to them in the function definition. To do that, in the parentheses of the function call, write the name of a parameter and assign the desired value to it. Do the same for each parameter. Separate them with commas. Here are two examples:
def getFullName(itemNbr, itemName, size, price): print("Item #: ", itemNbr) print("Name: ", itemName) print("Size: ", size) print("Marked Price: ", price) getFullName(size='M', price=124.95, itemNbr=972947, itemName="Balloon-Sleeve Wrap Midi Dress") print("------------------------------------------------------------") getFullName(itemName="Men's Infinite Stretch Solid Slim-Fit Pants", itemNbr=240_585, price=72.50, size="34x30") print("============================================================")
This would produce:
============================================================ Item #: 972947 Name: Balloon-Sleeve Wrap Midi Dress Size: M Marked Price: 124.95 ------------------------------------------------------------ Item #: 240585 Name: Men's Infinite Stretch Solid Slim-Fit Pants Size: 34x30 Marked Price: 72.5 ============================================================ Press any key to continue . . .
Default Arguments
Introduction
Consider the following code:
def price_evaluation(discountRate):
markedPrice = 125.00
discountedPrice = markedPrice * discountRate / 100;
finalPrice = markedPrice - discountedPrice;
print("Marked Price: ", markedPrice)
print("Discount Rate: ", discountRate)
print("Discounted Price: ", discountedPrice)
print("Final Price: ", finalPrice)
print("==================================")
print("Fun Department Store")
print("==================================")
price_evaluation(25)
print("-------------------------")
price_evaluation(15)
print("-------------------------")
price_evaluation(25)
print("-------------------------")
price_evaluation(35)
print("-------------------------")
price_evaluation(25)
print("==================================");
This would produce:
================================== Fun Department Store ================================== Marked Price: 125.0 Discount Rate: 25 Discounted Price: 31.25 Final Price: 93.75 ------------------------- Marked Price: 125.0 Discount Rate: 15 Discounted Price: 18.75 Final Price: 106.25 ------------------------- Marked Price: 125.0 Discount Rate: 25 Discounted Price: 31.25 Final Price: 93.75 ------------------------- Marked Price: 125.0 Discount Rate: 35 Discounted Price: 43.75 Final Price: 81.25 ------------------------- Marked Price: 125.0 Discount Rate: 25 Discounted Price: 31.25 Final Price: 93.75 ================================== Press any key to continue . . .
In some applications, almost every time you call a certain function, you usually pass the same value, in which case you pass a different value only sometimes. In this type of scenario, you can provide a default value to the parameter so that you would pass an argument only when it is different from the default value.
When creating a function whose parameter is passed with the same value almost every time, in the parentheses of the function, assign the desired default value to the parameter. Here is an example:
def price_evaluation(discountRate = 25):
# . . .
After doing this, whenever you call the function, if you want to pass the argument with the default value, you can omit it. If you call the function without the argument, the function would use the default value. Here are examples:
def price_evaluation(discountRate = 25):
markedPrice = 125.00
discountedPrice = markedPrice * discountRate / 100;
finalPrice = markedPrice - discountedPrice;
print("Marked Price: ", markedPrice)
print("Discount Rate: ", discountRate)
print("Discounted Price: ", discountedPrice)
print("Final Price: ", finalPrice)
print("==================================")
print("Fun Department Store")
print("==================================")
price_evaluation()
print("-------------------------")
price_evaluation(15)
print("-------------------------")
price_evaluation()
print("-------------------------")
price_evaluation(35)
print("-------------------------")
price_evaluation()
print("==================================")
Mixing Default arguments and Others
You can create a function that uses a mix of parameters that use default values or not. If you create a function that uses two parameters with only one with a default value, the parameter without a default value must come first. In the body of the function, you can ignore or use the parameters as you see fit. Here is an example:
def price_evaluation(markedPrice, discountRate = 25):
discountedPrice = markedPrice * discountRate / 100;
finalPrice = markedPrice - discountedPrice;
print("Marked Price: ", markedPrice)
print("Discount Rate: ", discountRate)
print("Discounted Price: ", discountedPrice)
print("Final Price: ", finalPrice)
When calling the function, you must provide at least a value for the parameter that doesn't use a default parameter. In this case, the function would use the default value for the other parameter. Still, if you want, you can pass a value for the default argument. Here are examples:
def price_evaluation(markedPrice, discountRate = 25):
discountedPrice = markedPrice * discountRate / 100;
finalPrice = markedPrice - discountedPrice;
print("Marked Price: ", markedPrice)
print("Discount Rate: ", discountRate)
print("Discounted Price: ", discountedPrice)
print("Final Price: ", finalPrice)
print("==================================")
print("Fun Department Store")
print("==================================")
price_evaluation(125.00)
print("-------------------------")
price_evaluation(125.00, 15)
print("-------------------------")
price_evaluation(245.85)
print("-------------------------")
price_evaluation(245.85, 35)
print("==================================")
This would produce:
================================== Fun Department Store ================================== Marked Price: 125.0 Discount Rate: 25 Discounted Price: 31.25 Final Price: 93.75 ------------------------- Marked Price: 125.0 Discount Rate: 15 Discounted Price: 18.75 Final Price: 106.25 ------------------------- Marked Price: 245.85 Discount Rate: 25 Discounted Price: 61.4625 Final Price: 184.3875 ------------------------- Marked Price: 245.85 Discount Rate: 35 Discounted Price: 86.0475 Final Price: 159.8025 ================================== Press any key to continue . . .
If you want to create a function that uses three or more parameters with one of them having a default value, in the parentheses of the function, the parameter without a default value must come first. When calling the function, you must provide a value for each of the parameters that don't use default values. Here is an example:
def price_evaluation(itemName, markedPrice, discountRate = 25): discountedPrice = markedPrice * discountRate / 100; finalPrice = markedPrice - discountedPrice; print("Item Name: ", itemName) print("Marked Price: ", markedPrice) print("Discount Rate: ", discountRate) print("Discounted Price: ", discountedPrice) print("Final Price: ", finalPrice) print("===========================================================================") print("Fun Department Store") print("===========================================================================") price_evaluation("Khaki Pants", 45.50) print("---------------------------------------------------------------------------") price_evaluation("Women's Croft & Barrow® Print Twist-Front Midi Dress", 88.55, 15) print("---------------------------------------------------------------------------") price_evaluation("Everyday Straight Jeans in Regular, Slim & Husky", 22.25) print("---------------------------------------------------------------------------") price_evaluation("Women's Leather High Heels", 115.75, 35) print("===========================================================================")
This would produce:
=========================================================================== Fun Department Store =========================================================================== Item Name: Khaki Pants Marked Price: 45.5 Discount Rate: 25 Discounted Price: 11.375 Final Price: 34.125 --------------------------------------------------------------------------- Item Name: Women's Croft & Barrow® Print Twist-Front Midi Dress Marked Price: 88.55 Discount Rate: 15 Discounted Price: 13.2825 Final Price: 75.2675 --------------------------------------------------------------------------- Item Name: Everyday Straight Jeans in Regular, Slim & Husky Marked Price: 22.25 Discount Rate: 25 Discounted Price: 5.5625 Final Price: 16.6875 --------------------------------------------------------------------------- Item Name: Women's Leather High Heels Marked Price: 115.75 Discount Rate: 35 Discounted Price: 40.5125 Final Price: 75.2375 =========================================================================== Press any key to continue . . .
Using Many Default Arguments
If you are creating a function with three parameters with two of them with default values, in the parentheses, the parameter without the default value must come first. Here is an example:
def price_evaluation(origPrice, discountRate = 25, taxRate = 7.25):
. . .
When calling the function, you can pass just one argument, in which case, the function would use the default values of the second parameters. If you call the function with two arguments, the values would be used for the first and the second parameter. Otherwise, you can call the function with all three parameters. Here are examples:
def price_evaluation(origPrice, discountRate = 25, taxRate = 7.25):
discountAmount = origPrice * discountRate / 100;
priceAfterDiscount = origPrice - discountAmount;
taxAmount = priceAfterDiscount * taxRate / 100;
finalPrice = priceAfterDiscount - taxAmount;
print("Original Price: ", origPrice)
print("Discount Rate: ", discountRate)
print("Discount Amount: ", discountAmount)
print("Price after Discount: ", priceAfterDiscount)
print("Tax Rate: ", taxRate)
print("Tax Amount: ", taxAmount)
print("Final Price: ", finalPrice)
print("=========================================")
print("Fun Department Store")
print("=========================================")
price_evaluation(45.50)
print("-----------------------------------------")
price_evaluation(88.55, 15)
print("-----------------------------------------")
price_evaluation(225.25, 50, 5.75)
print("=========================================")
Thi would produce:
========================================= Fun Department Store ========================================= Original Price: 45.5 Discount Rate: 25 Discount Amount: 11.375 Price after Discount: 34.125 Tax Rate: 7.25 Tax Amount: 2.4740625 Final Price: 31.6509375 ----------------------------------------- Original Price: 88.55 Discount Rate: 15 Discount Amount: 13.2825 Price after Discount: 75.2675 Tax Rate: 7.25 Tax Amount: 5.456893750000001 Final Price: 69.81060624999999 ----------------------------------------- Original Price: 225.25 Discount Rate: 50 Discount Amount: 112.625 Price after Discount: 112.625 Tax Rate: 5.75 Tax Amount: 6.4759375 Final Price: 106.1490625 ========================================= Press any key to continue . . .
The real rule is that if you are creating a function with many parameters with some parameters having default values, in the parentheses, the parameters without the default values must come first.
As seen in the section about named arguments, if you are calling a function that has one or more default arguments, you can use the name of each parameter when calling the function. This means that if you provide a name for an argument, you must specify the name of each argument whose value you provide. Here are examples:
print("============================================================")
def price_evaluation(origPrice, discountRate = 25, taxRate = 7.25):
discountAmount = origPrice * discountRate / 100;
priceAfterDiscount = origPrice - discountAmount;
taxAmount = priceAfterDiscount * taxRate / 100;
finalPrice = priceAfterDiscount - taxAmount;
print("Original Price: ", origPrice)
print("Discount Rate: ", discountRate)
print("Discount Amount: ", discountAmount)
print("Price after Discount: ", priceAfterDiscount)
print("Tax Rate: ", taxRate)
print("Tax Amount: ", taxAmount)
print("Final Price: ", finalPrice)
print("=========================================")
print("Fun Department Store")
print("=========================================")
price_evaluation(origPrice=45.50)
print("-----------------------------------------")
price_evaluation(discountRate = 15, origPrice=88.55)
print("-----------------------------------------")
price_evaluation(origPrice=225.25, taxRate = 5.75, discountRate = 50)
print("=========================================")
Practical Learning: Ending the Lesson
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