13. Function arguments

We have seen that, when there are more than one type of objects in Reeborg's World, we must sometimes specify which object Reeborg must take or put down by using a function argument as in:

take("token")
put("star")

However, we have not seen yet how to define such a function. It is actually fairly easy: all we have to do is include a variable as an argument between the parentheses when defining the function. For example, suppose we want to define a function turn() that would take a number as its argument so that the number indicates the number of left turn we want Reeborg to make. Thus turn(1) would correspond to a single left turn whereas turn(3) would correspond to three left turns (which, as we know, amounts to having Reeborg make a right turn). One way to do this is as follows:

def turn(number):
    for _ in range(number):
        turn_left()

Your turn!

Define such a turn function and try it out in a program.

13.1. Many arguments

If you recall, print() can take more than one argument, with each argument separated by a comma. You can probably guess how we can define a similar function:

def my_function(argument_1, argument_2, ...):
   # code block

Suppose that, like above, we want to be able to specify a number of turns ... and also a number of moves ... and a number of whatever. We could define a function like turn for each type of repeated action; however, there is a more general way which only requires to define a single function, which we will call my_repeat (repeat would have been a better name, but it's a special Reeborg keyword). Here's a possible definition:

def my_repeat(function, number):
    for _ in range(number):
        function()

So, if we call it with turn_left and 3 as arguments:

my_repeat(turn_left, 3)

it will be interpreted as:

for _ in range(3):   # number is replaced by 3
    turn_left()      # function is replaced by turn_left

which we recognize as our familiar turn_right equivalent. However, having defined my_repeat we can use it with different numbers and functions, such as:

my_repeat(move, 4)   # move 4 steps

Your turn!

Define such a my_repeat function and try it out in a program.

مهم

Unlike print(), which can take an arbitrary number of arguments, the functions we have defined so far will always require a set number of arguments (1 for turn, 2 for my_repeat). You should check what happens if you give a different number of arguments than what was indicated when defining the function.

Creating functions which can accept an arbitrary number of arguments is something which we will see later, after we have seen a few other concepts.