Setup and First Script

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When to use it.

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Python scripting is a easy and efficient way to extend Unreal Engine abilities. Based on my usage I would recommend using Python scripting when:

• We prefer to use Python over C++ (note that Python scripts aren’t as fast as C++ and should not be used in core gameplay).
• We need editor time tool using external libraries that python may provide.
• We need to use some python based libraries.
• Python libs are more robust and performance isn’t huge issue.

This means I would suggest using python scripting mostly in Editor time (time when we work on editor) to generate content (for instance using PCG), generating some data for analysis, importing and exporting data, or any other tools that may use robust python pros like data analysis, text manipulating or web connection. If you want to use python during Play time (during playing cooked build) I would recommend to use it only async but that(Play time python script calling) is not supported currently.

Note that I am not aware of most python libraries that can be really useful so don’t limit your ideas by my examples of usage.

Setting it Up

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To setup Python in unreal we need to complete simple step list:

Enable Python Scripting plugin

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1. Firstly we are creating some basic project. I have chosen ThirdPerson Template with base in C++(C++ base would be recommended for this blog)

   

2. Then we enable Python Plugin in by selecting Edit > Plugins > Python Editor Script Plugin, after enabling it will cause editor to ask for restart. To it to be able to proceed to next step
3. After this step we should enable Python Developer Mode in editor settings. To do this we can simply tick box in Edit > Editor Settings > Plugins > Python and tick developer mode checkbox. You can simply type Developer Mode in search bar too. Checking it make editor to ask for restart let do it.
4. We should have Python enabled and ready to work with, to confirm if Developer Mode which makes writing python ue5 scripts easily we can check if in path Intermediate\PythonStub we have file unreal.py this file contains unreal bindings for python and regenerate every time we open Editor not when we refresh project c++ files!

Create friendly environment

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For our quality of life we should setup some python IDE, you can go with whatever IDE you like, I will go with VsCode. I will not go over installing VsCode as this should be straight forward and there is a lot of tutorial for it.

In VsCode we should install Python and Pylence extensions.

Then we will create our first python script file, the cool thing is that we can choose whatever path we want as we will be providing Unreal it path. So I will create new folder only for python scripts (this is only to show we can, usually in work or project you want to keep in source versioning system).

After creating new file usually Vscode will ask for python interpreter, to make it go smoothly I would recommended choosing the one unreal is providing. This one won’t be showing in Vscode and we need to find it manually. The path for interpreter should be {EnginePath}\\Engine\\Binaries\\ThirdParty\\Python3\\Win64\\python.exe.

Then if we start typing we will see big issue. After creating simple code

import unreal #importing unreal module

unreal. #presing auto completion

We don’t get any suggestions. To fix that we need to add external unreal.py form project’s Intermediate\PythonStub to VsCode python extension. Do do so we should go to settings and type python.analysis.extraPaths then add our path to Intermediate\PythonStub folder, adding path to unreal.py won’t work.

After this we should have fully python ide support. Lets try writing some simple script and running it.

First script

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Our first script will be simple one that prints all asset names in our project

import unreal

asset_registry = unreal.AssetRegistryHelpers.get_asset_registry()
for asset in asset_registry.get_all_assets():
    print(asset.get_full_name())

Of course we could define functions, classes and so one but we won’t bother with it at this time. Now we need to test it by execution.

Running Script

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We have multiple way to run it I will show you for most crucial ones:

Running it from command line

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this enables you to execute scripts when editor is closed, and this will work well with CD/CI like jenkins. To run script we can simply open terminal and type <PathToEngine>\\Binaries\\Win64\\UnrealEditor-Cmd.exe <PathToProject> -run=pythonscript -script=<PathToScript>. For me it looked like this:

• PathToScript == D:\\UE5_proj\\PythonScripts\\ListAllAssets.py
• PathToProject == D:\\UE5_proj\\PythonBlogProject\\PythonBlogProject.uproject
• PathToEngine == Z:\\Games\\EpicGames\\UE_5.2\\Engine

and final command in terminal would looks like this:

Z:\\Games\\EpicGames\\UE_5.2\\Engine\\Binaries\\Win64\\UnrealEditor-Cmd.exe D:\\UE5_proj\\PythonBlogProject\\PythonBlogProject.uproject -run=pythonscript -script=D:\\UE5_proj\\PythonScripts\\ListAllAssets.py

This will run and generate either fail or success information, we are looking for information like:

LogPythonScriptCommandlet: Display: Python script executed successfully
LogInit: Display: Success - 0 error(s), 0 warning(s)

But wait, we actually didn’t printed anything !? That is correct UnrealEditor-Cmd.exe isn’t pushing any logs that we create, our prints, logs and so on are hidden in <ProjectPath>\\Saved\\Logs\\ and we can see all assets we have in project. small sample of it

LogPython: /Script/Engine.MaterialFunction /Engine/Functions/Engine_MaterialFunctions02/Utility/MakeFloat2.MakeFloat2
LogPython: /Script/Engine.Texture2D /Engine/EngineSky/VolumetricClouds/CloudGradientTexture.CloudGradientTexture
LogPython: /Script/Engine.Texture2D /Engine/EngineSky/VolumetricClouds/CloudWeatherTexture.CloudWeatherTexture
LogPython: /Script/Engine.Texture2D /Engine/EngineSky/VolumetricClouds/T_NoiseErosion.T_NoiseErosion
LogPython: /Script/Engine.VolumeTexture /Engine/EngineSky/VolumetricClouds/T_VolumeNoiseErosion32.T_VolumeNoiseErosion32
LogPython: /Script/Engine.Texture2D /Engine/EngineSky/VolumetricClouds/T_NoiseShape64.T_NoiseShape64
LogPython: /Script/Engine.VolumeTexture /Engine/EngineSky/VolumetricClouds/T_VolumeNoiseShape64 T_VolumeNoiseShape64
LogPython: /Script/Engine.Material /Engine/EngineSky/VolumetricClouds/m_SimpleVolumetricCloud.m_SimpleVolumetricCloud
LogPython: /Script/Engine.MaterialInstanceConstant /Engine/EngineSky/VolumetricClouds/m_SimpleVolumetricCloud_Inst.m_SimpleVolumetricCloud_Inst
LogPython: /Script/Engine.StaticMesh /Engine/EngineMeshes/Sphere.Sphere
LogPython: /Script/Engine.Texture2D /Engine/EngineResources/WhiteSquareTexture.WhiteSquareTexture
LogPython: /Script/Engine.Texture2D /Engine/EngineResources/GradientTexture0.GradientTexture0
LogPython: /Script/Engine.Texture2D /Engine/EngineResources/Black.Black
LogPython: /Script/Engine.MaterialFunction /Engine/Functions/Engine_MaterialFunctions02/Utility/BreakOutFloat3Components.BreakOutFloat3Components
LogPython: /Script/Engine.MaterialFunction /Engine/Functions/Engine_MaterialFunctions02/Utility/MakeFloat3.MakeFloat3
LogPython: /Script/Engine.MaterialFunction /Engine/Functions/Engine_MaterialFunctions02/Utility/MakeFloat4.MakeFloat4

Running it from editor

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This need only path to script:

• PathToScript == D:\\UE5_proj\\PythonScripts\\ListAllAssets.py
• Open Editor

Note that we can give unreal path to scripts and that way we can forget about whole path. (Work in progress) In editor we need to two things:

• open output log -> we do this by going window > Output log
• selecting proper command line

After this we can simply past our script path into command line and press enter. Note as we are listing all assets it may take some time!

Running form command line with editor start-up

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This is enable us to rung editor from command line and execute script on it, similar to Running it from command line we just need terminal command.

<PathToEngine>\\Binaries\\Win64\\UnrealEditor-Cmd.exe <PathToProject> -ExecutePythonScript="<PathToScript>"

in our example that will be:

Z:\\Games\\EpicGames\\UE_5.2\\Engine\\Binaries\\Win64\\UnrealEditor-Cmd.exe D:\\UE5_proj\\PythonBlogProject\\PythonBlogProject.uproject -ExecutePythonScript="D:\\UE5_proj\\PythonScripts\\ListAllAssets.py"

After running script our Editor will turn off and results will be in log file same as in Running it from command line.

Running form blueprint

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To quickly run command in engine from blueprint we need to create either Editor Utility Blueprint or Editor Utility Widget. I have chosen Editor Utility Blueprint that is child of EditorUtilityObject and for now I recommend you to do the same. In this blueprint we create function that can be called in editor, let name it List all assets. In this we have couple of options:

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  - this is just checking if python is supported.

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  - this is mainly to create some python code in string and execute this script. We won’t use it for our script

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  - this is simple node to execute python script provided in as path to script (for me it was D:\\UE5_proj\\PythonScripts\\ListAllAssets.py)

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  - this one provide more possible inputs and outputs. String can be either command like print("It works!") or path to script like D:\\UE5_proj\\PythonScripts\\ListAllAssets.py by picking right ExecutionMode.

All inputs are:

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• PythonCommand - path or script to call
• ExecutionMode - how given PythonCommand should be interpreted possible values:
  • ExecuteFile - Execution file at path given in PythonCommand (works with single commands too like print("Working!"))
  • ExecuteStatement - Execute statement given in PythonCommand and logs result (don’t works with path to file)
  • EvaluateStatement - Execute statement given in PythonCommand and return result (don’t works with path to file)
• FileExecutionScope - how given PythonCommand should be interpreted possible values:
  • Private - Execution happens in isolated environment (all imports won’t affect other script)
  • Public - Execution happens in global environment (all imports will affect other public scripts)

All output are:

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• Command Result - this will return only if Command is evaluating some value that is not consumed (by printing for instance). This will be '' for command print("working!") and will return 'working!' for command "working!". This will contain error if script fails!

• Log Output - this contains array of logs that are containing log message as well as log type:

• Return Value - this return true if script run successfully and false if it failed

After creating some script (any presented here) we can simply override Run function of our Blueprint and pin our function.

Sources

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• https://docs.unrealengine.com/5.2/en-US/scripting-the-unreal-editor-using-python/
• https://youtu.be/D-mDLwNawVU
• https://ryandowlingsoka.com/unreal/python-in-unreal/

End

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Thanks for attention, next time I will show how we can use python in more useful way and how to expose our custom C++ class to use in python.