Category: Minecraft

Python in Minecraft 10 – functions and modules

Importing modules

In the previous python in minecraft blog we created a program to construct an east-west tunnel. This is a useful program which we might want to use often. We can put the program into a function and save the function in a module so it can be used by other programs. We will call the function “buildEastTunnel()”. The module name will be just the name of the file, which in this case we will call “”. Then whenever we want to build a tunnel running east west, we can import the module just like we have been importing mcpi.minecraft and mcpi.block.

There are several ways to import functions. The simplest method imports the module but not the function name. We still need to tell python to look in that module when calling the function

import tunnel

If you want to give the module a better name you can use “as” to assign a new name. This is what we do when importing mcpi.minecraft as minecraft.

import tunnel as mole

If you want to use the function without qualifying it with the module name each time, you can import the function explicitly from the module.

from tunnel import buildEastTunnel

Function parameters

Now calling buildEastTunnel() as it is currently written will always construct a tunnel in the same place, x = -400 to -200, y = 72 at each end, z = 244. However, if we design the function to take parameters then when we call the function we can specify where the tunnel is built.

def buildEastTunnel(mc, x1, x2, y1, y2, z):
    """Builds an east-west tunnel (in the x direction)"""
    # rest of function ...

import mcpi.minecraft as minecraft
from tunnel import buildEastTunnel
mc = minecraft.Minecraft.create()
buildEastTunnel(mc, 0, 200, 75, 75, 233)

This example passes the mc object to the function so it knows which minecraft server to build the tunnel in. Then it gets the x, y and z coordinates at each end of the tunnel. Because the tunnel is running east-west there is only one z value required. Our code is designed to go from xmin to xmax but someone calling our function might put the higher value of x first and the lower value second or vice versa. We can take advantage of python’s ability to assign several variables at once to ensure xmin is less than xmax.

def buildEastTunnel(mc, x1, x2, y1, y2, z):
    """Builds an east-west tunnel (in the x direction)"""
    if x1 < x2:
        xmin, yatxmin, xmax, yatxmax = x1, y1, x2, y2
        xmin, yatxmin, xmax, yatxmax = x2, y2, x1, y1
    # rest of function ...

When designing a function to take parameters, it is possible to specify some parameters as “required” and other parameters as “optional”. Optional parameters need to be given a default value. In our example it would be useful for the y values to use ground level if it is not supplied. “Required” parameters have to come before “optional” parameters so the parameters list should now be (mc, x1, x2, z, y1, y2).

def buildEastTunnel(mc, x1, x2, z, y1=None, y2=None):
    """Builds an east-west tunnel (in the x direction)"""
    if x1 < x2:
        xmin, yatxmin, xmax, yatxmax = x1, y1, x2, y2
        xmin, yatxmin, xmax, yatxmax = x2, y2, x1, y1
    if yatxmin == None:
        yatxmin = getGroundHeight(mc, xmin, z)
    if yatxmax == None:
        yatxmax = getGroundHeight(mc, xmax, z)
    # rest of function ...

Finding ground height

We are calling a function getGroundHeight(mc,x,z) which we haven’t written yet. In mcpi.minecraft is a function mc.getHeight(x,z) which finds the highest block which is not air at x and z coordinates. Unfortunately that block will often be a tree or sapling. Here is a function which corrects mc.getHeight(x,z) for trees. It makes use of the mc.getBlock(x,y,z) function which returns the id of the block at those coordinates.

def getGroundHeight(mc, x, z):
    """finds heighest non air block which is also not a tree or sapling"""
    LEAVES2 = block.Block(161)
    y = mc.getHeight(x, z)
    while mc.getBlock(x, y, z) in (,,,,
        y -= 1
    return y
Categories: CoderDojo, Minecraft

CoderDojo – Minecraft with Python – setup

Minecraft Pi on the Raspberry Pi can be controlled using python scripts. Here we will set up a Mac, Linux or Windows PC to achieve the same functionality by using the RaspberryJuice plugin with the Spigot Minecraft server.



Installation of Java, Git and Minecraft is straight forward following instructions from sites listed above. Installing Git provides a bash shell for Windows.

Python installation

When downloading python, choose Python 3 not Python 2.

When installing python, tick the check box to add python to the path. This makes it easier to run python from the command line, although you will normally run python by starting the application called IDLE. Then click on “Install Now”

To run python on the command line, the command is python3 on Mac and Linux and python on Windows. I will use python3 in these instructions.

Windows only – python installation

To make python3 work in the bash shell on windows, start Git-Bash and type the following command:

echo "alias python3='winpty python.exe'" >> .bashrc

The winpty is required to enable python interactive interpreter to work in git-bash the same way it works in Windows command prompt, so this alias is providing two solutions in one line. Now quit git-bash (by typing exit). Restart git-bash and type python3. You should see something like the following:

$ python3
Python 3.6.2 (v3.6.2:5fd33b5, Jul  8 2017, 04:57:36) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.

If you forgot to click the check box to add python to the path when installing python then it can be added later by going to Control Panel > Uninstall a program and double clicking on the Python program which will be called Python 3.6.2 (64-bit) or similar. Select “Modify” to change your original setup. You don’t need to change the Optional Features so click “Next”. In the Advanced Options click the checkbox now called “Add Python to environment variables” and then click on “Install”.

Spigot minecraft server installation using bash shell

To install Spigot server, use the installer caller BuildTools.jar available from . Download this file and put it in a folder you want to install the Spigot minecraft folder, then run it using java.

These instructions show how to install using bash shell. You don’t have to use bash shell, but by using bash shell the same instructions work for all platforms. Bash shell is available on Mac OS X (Terminal), Linux (command line or Terminal) or Windows (Git-bash is available after you installed git above).

mkdir minecraft-spigot
mv Downloads/BuildTools.jar minecraft-spigot/
cd minecraft-spigot
java -jar BuildTools.jar

Now edit the file eula.txt and change eula=false to eula=true . This is to acknowledge that you agree with the EULA which is necessary to run the server. You can do this with a text editor from the GUI such as Windows NotePad or Mac TextEdit. Alternatively do it from the command line using vi text editor

vi eula.txt

The vi commands are cryptic. When you start vi you will be in command mode. Use the arrow keys to move the cursor to the line you want to change. Then press the [a] key which is the command to put vi in edit (append) mode. In edit mode you can move the cursor to the word false, delete it with the [delete] key and type in true. To get out of edit mode and back into command mode, press the [ESC] key. You now have to issue the command to write the changed file, and quit vi, which is pressing the following four keys [:][w][q][Enter] .

Return to original directory ready for next step.

cd ..

Install RaspberryJuice

You can get the RaspberryJuice plugin from using Git.

git clone
mkdir -p minecraft-spigot/plugins
cp RaspberryJuice/jars/RaspberryJuice-1.9.jar minecraft-spigot/plugins/

Run Spigot Server

Using Terminal or Command Prompt from the minecraft-spigot folder. Your spigot version number may be different.

cd minecraft-spigot
java -jar spigot-1.12.jar

To stop the server, type


as a server command.

You should now have a configuration file in the RaspberryJuice folder in the plugins folder called config.yml. I like to edit that file and change the

location: RELATIVE
location: ABSOLUTE

RELATIVE makes RaspberryJuice behave the same way as Python on Minecraft Pi which uses coordinates relative to the spawn point. However on PCs it is easier to use ABSOLUTE coordinates which equate to the coordinates visible using F3 in Minecraft.

To prepare for the next section, change back up a directory to where we first started.

cd ..
Python mcpi module for RaspberryJuice

To write python scripts you need to install the mcpi module. You can choose the original one, exactly as supplied for Minecraft Pi or the modded one which adds some additional commands. I prefer the modded one. They are included in the files you cloned from github.

The following command tells you where user site-packages should be installed.

python3 -m site --user-site

Use this information to link to the module in the git repository you downloaded. This has to be done for each user on computer who will want to run python scripts.

Mac or Linux using Bash

PKGDIR=`python3 -m site --user-site`
mkdir -p "$PKGDIR"
cd "$PKGDIR"
ln -s "${STARTDIR}/RaspberryJuice/src/main/resources/mcpi/api/python/modded/mcpi"

Windows command prompt – run as administrator

for /f %a in ('python -m site --user-site') do set PKGDIR=%a
mkdir %PKGDIR%
mklink /D mcpi %HOMEPATH%\RaspberryJuice\src\main\resources\mcpi\api\python\modded\mcpi

Now start the spigot server

cd minecraft-spigot
java -jar spigot-1.12.jar

In another bash shell, create a python script to send a chat message. Here is command using vi.

import mcpi.minecraft as minecraft
mc = minecraft.Minecraft.create()

Run this script and you should see your message in the first bash shell.

Troubleshooting for Windows

The following tests should be done in Git-Bash:

1. Type python --version. It should return “Python 3.6.2” or similar. If it says “bash: python: command not found” then you have not ticked “Add python to PATH” when installing. See Windows only python installation instructions above for remedy.

2. Type python3. It should start the python interpreter shell ending with >>>. If you not then you haven’t created the .bashrc file correctly. See Windows only python installation instructions. You can delete the existing .bashrc file in your home directory and try creating it again. Be extremely careful with spaces and using the correct type of quotation marks. It is best if you can copy and paste directly from this web site into Git-Bash. To paste in Git-Bash, right click the mouse and select “Paste”.

3. Once you are in the python interpreter shell, type import mcpi.minecraft. If there is an error then there is a problem with the link you created in “Python mcpi module for RaspberryJuice”. Try creating it again.

Categories: CoderDojo, Minecraft