Functions
Functions are subroutines that return one or more values to the main program. If a subroutine changes the value of a variable used elsewhere in the program then it should be a
function not a procedure. Functions can also take parameters. The return value or values can be the same values passed in or different ones.
Defining a function
We could make a function add_two_nums that returns the result of adding them instead of printing the sum.
Example 1
def add_two_nums(num1,num2):
total = num1 + num2
return total |
Example 2
def add_name(names_list):
name = input("Enter the name of the new team member: ")
names_list.append(name)
return names_list |
function defining syntax rules:
- Def is in lower case at the start of the procedure
- A suitable identifier has been selected
- There are brackets that may or may not contain parameters to be passed in
- There is a colon on the end of the def line
- All the code to be executed when the subroutine
is called is indented under the def line
- The last line of the function returns one or more values to the main program
Calling a function
Like a procedure, a function is called by its identifier followed by empty brackets or brackets containing any arguments passed in. Passing the wrong number of arguments will result in an error.
By far the most important thing to remember when calling a function is it must be given somewhere to store any return values. Our example functions above may be called an used as shown below.
first = int(input("Enter a number: ""))
second = int(input("Enter a number: "))
result = add_two_nums(first, second)
print(f"{first} + {second} = {result}") |
This returns the result of adding two numbers to the variable total. It is possible to use the same name for a variable passed in as an argument and the parameter but I have avoided that so as to be clear
that the parameter is the name defined in the subroutine as a parameter and it shows how and where that value will be used while the actual value passed is the argument.
team = ["Bob","Jim","Sam"]
team = add_name(team) |
The code above accepts the team list from the main program to use in the subroutine and returns the updated list after it is run.
Syntax checker
Fix the code below so the subroutine takes two integer inputs and outputs whether the first is a multipe of the second e.g. if the user enters 18 and then 3 the output will be 'This is a multiple'.
| def add_name(names): # def not sub |
| new_name = input("Enter the name of a new person: ") # indentation fixed |
| if new_name not in names: # indentation corrected and condition fixed |
| names.append(new_name) # indentation fixed |
| else: # indentation fixed |
| print(f"{new_name} is already in the list") # indentation fixed |
| return names # indentation fixed |
| team = ["Bob","Jim","Sam"] |
| team = add_name(team) # the new team must be returned |