A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

A function can return data as a result.

Creating a Function

In Python a function is defined using the def keyword:

Example

def my_function():
  print("Hello from a function")

Calling a Function

To call a function, use the function name followed by parenthesis:

def my_function():
  print("Hello from a function")

my_function()

Output

Parameters

Information can be passed to functions as parameter.

Parameters are specified after the function name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma.

The following example has a function with one parameter (fname). When the function is called, we pass along a first name, which is used inside the function to print the full name:

def my_function(fname):
  print(fname + " Refsnes")

my_function("Emil")
my_function("Tobias")
my_function("Linus")

Output

Default Parameter Value

The following example shows how to use a default parameter value.

If we call the function without parameter, it uses the default value:

def my_function(country = "Norway"):
  print("I am from " + country)

my_function("Sweden")
my_function("India")
my_function()
my_function("Brazil")

Output

Return Values

To let a function return a value, use the return statement:

def my_function(x):
  return 5 * x

print(my_function(3))
print(my_function(5))
print(my_function(9))

Output