Getting data out of functions¶
Parameters: Enable getting data into functions
Return values: Enable getting data out of functions - think of it as the result of a function
Let's think about examples from functions we've called:
name = input("What is your name? ")
name_length = len(name)
print(name,"has",name_length,"letters")
input() returns a string (whatever the user typed) and we saved that result to name
len() returns an integer (the length of the string name) and we saved that result to name_length
print() doesn't return anything - we never see print on the right side of an =
Syntax for returning values¶
To return a value from a function you've defined, put the return statement somewherer in your function
- keyword
return - an expression (i.e., a value, a variable, mathematical operation, or anything that results in a value)
def f_to_c(fahrenheit_temp):
celsius_temp = (fahrenheit_temp-32)*(5/9)
return celsius_temp
f_reading = float(input("Enter fahrenheit reading: "))
c_temp = f_to_c(f_reading)
print(c_temp)
Because f_to_c() returns something, we can save its result to c_temp
Note that the return statement will cause the function to end - even if it is in the middle of the function, so you usually find it at the end of a function.
Returned values can be used anywhere the value itself could be used¶
print("100F is",f_to_c(100),"in Celsius.")
kelvin_reading = 273.15 + f_to_c(100)
print("In Kelvin, it is",kelvin_reading)
Why should you return instead of just printing the result?¶
Returning values gives you more flexibility in how the function can be used.
Consider the pay calculator. We might want to allow a user to interact with it to check their pay; or, we might read employee information from a file so that we can process all their paychecks.
import csv
def calculate_pay(wage,hours):
if hours <= 40:
pay = wage*hours
else:
overtime_hours = hours-40
pay = (wage*40) + (wage*1.5*overtime_hours)
return pay
def user_pay_calculator():
hourly_wage = float(input("Enter your hourly wage: "))
num_hours = float(input("Enter your number of hours worked: "))
print("Your total pay is",calculate_pay(hourly_wage,num_hours))
def process_payroll(employee_hours_logged_filename):
with open(employee_hours_logged_filename) as hours_log_file:
employees_log = csv.reader(hours_log_file)
employees_log = list(employees_log)
counter = 0
while counter < len(employees_log):
print(employees_log[counter][0],":",calculate_pay(float(employees_log[counter][1]),float(employees_log[counter][2])))
counter += 1
#user_pay_calculator()
process_payroll("emp_hours_log_2021_June20-26.csv")