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  • 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.

Arbitrary Arguments, *args

If the number of arguments is unknown, add a * before the parameter name:

def my_function(*kids):
  print("The youngest child is " + kids[2])

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

Keyword Arguments

You can also send arguments with the key = value syntax.

def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Emil", child2 = "Tobias", child3 = "Linus")

Arbitrary Keyword Arguments, **kwargs

If you do not know how many keyword arguments that will be passed into your function, add two asterisk: ** before the parameter name in the function definition.

This way the function will receive a dictionary of arguments, and can access the items accordingly:

def my_function(**kid):
  print("His last name is " + kid["lname"])

my_function(fname = "Tobias", lname = "Refsnes")

Default Parameter Value

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

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


return and pass

  • To let a function return a value, use the return statement
  • function definitions cannot be empty, but if you for some reason have a function definition with no content, put in the passstatement to avoid getting an error.
def myfunction():


  • Python also accepts function recursion, which means a defined function can call itself.
  • Recursion is a common mathematical and programming concept. It means that a function calls itself. This has the benefit of meaning that you can loop through data to reach a result.
  • The developer should be very careful with recursion as it can be quite easy to slip into writing a function which never terminates, or one that uses excess amounts of memory or processor power. However, when written correctly recursion can be a very efficient and mathematically-elegant approach to programming.

In this example, tri_recursion() is a function that we have defined to call itself ("recurse"). We use the k variable as the data, which decrements (-1) every time we recurse. The recursion ends when the condition is not greater than 0 (i.e. when it is 0).

To a new developer it can take some time to work out how exactly this works, best way to find out is by testing and modifying it.

def tri_recursion(k):
  if(k > 0):
    result = k + tri_recursion(k - 1)
    result = 0
  return result

print("\n\nRecursion Example Results")
Recursion Example Results