Functions

Introduction

In this tutorial we are going to create a few houses for our village.

To do this we will learn to use functions to packaged up our code into reusable chunks. We will also learn to save our code in Python modules so that we don’t need to typing or pasting code all of the time.

Simple Function

A function is a named block of code with some parameters and a return value. Parameters are variables that are set by the code that calls the function. The return value is passed back to the calling code.

Try typing (or pasting) this very simple function

def age(birth_year, current_year=2022):
    calculated_age = current_year - birth_year
    return calculated_age

When you hit enter after typing the function definition above nothing appears to happen. But you have created a function which you can now call like this:

my_age = age(1965)
print(my_age)

If you substitute your own birth_year value this function will print your age at the end of the year 2022.

age(1965) calls the function defined above and passes 1965 for the value of birth_year. It does not pass a value for the parameter current_year. The default value for current_year was set to 2022.

The function performs a - subtraction operation, taking the value of current_year and subtracting the value of birth_year. The result is assigned into calculated_age with =.

The function uses return to pass the value of calculated_age back to the caller. Our caller assigns the returned value to a variable called my_age and prints it out.

Now if you don’t want to use the default of 2022 (when this tutorial was written) you can pass your own value for current_year. e.g. to find out how old you were when the first Apple Mac was released:

print(age(1965, current_year=1984))
19

Obviously if unlike me, you were born after 1984 you would get a negative result.

Variable Naming

Notice the use of _ in the variable names. This is used to separate words in the variable name. Typically variable names are lowercase with words separated by underscores. It is also legal to use uppercase letters and numbers in variable names (but a number must not be the first character).

Tower Function

Lets create a function that will create a tower. We are going to use the following function. Don’t type it in yet, we are going to create a file for it. Also do not worry too much about the details of this function yet but notice that it has the following parameters that the caller can supply:

height - the height of the tower
width - the width of the tower
world - a world object that we can use to create blocks in the world
pos - the position of the tower

from mciwb import Direction, Item, Vec3


def tower(world, pos, width=5, height=8):
    """
    Create a tower of blocks at a given position.
    """

    # make sure the caller passed a variable of type Vec3 for pos
    assert isinstance(pos, Vec3)

    # each tower's wall is one less that width steps away from its opposite
    opposite = width - 1

    # outer loop does the layers of the tower
    for layer in range(height):

        y_offset = Direction.UP * layer

        # inner loop does the blocks in each of 4 walls
        for i in range(width):

            # calculate the position i steps to the east of pos
            eastward = pos + Direction.EAST * i + y_offset
            # front wall of tower
            world.set_block(eastward, Item.COBBLESTONE)
            # back wall of tower
            world.set_block(eastward + Direction.NORTH * opposite, Item.COBBLESTONE)

            # calculate the position i steps to the north of pos
            northward = pos + Direction.NORTH * i + y_offset
            # left wall of tower
            world.set_block(northward, Item.COBBLESTONE)
            # right wall of tower
            world.set_block(northward + Direction.EAST * opposite, Item.COBBLESTONE)

TODO continue