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Python Functions


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:

Example

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

my_function()
Run example »

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:

Example

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

my_function("Emil")
my_function("Tobias")
my_function("Linus")
Run example »


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:

Example

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

my_function("Sweden")
my_function("India")
my_function()
my_function("Brazil")
Run example »

Return Values

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

Example

def my_function(x):
  return 5 * x

print(my_function(3))
print(my_function(5))
print(my_function(9))
Run example »

Test Yourself With Exercises

Exercise:

Create a function named my_function.

:
  print("Hello from a function")

Start the Exercise