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Automating workflows using Python in Unreal Editor

5 min read

From: hu-po

Python scripting in Unreal Engine 5 and 5.1 is primarily used within the Unreal Editor to automate tasks and build robust content pipelines, rather than for in-game execution within a built executable [00:30:07].

Why Use Python for Automation?

Python has become a de facto language for production pipelines, a trend expected to grow with the rise of deep learning and generative AI models [01:00:00]. It is considered one of the easiest programming languages [01:36:00].

Key advantages for automation include:

  • Ease of Use Python is easy to learn and use for scripting [01:36:00].
  • Workflow Automation It’s a great choice for automating workflows [01:31:00].
  • Large-Scale Asset Management Python makes it easier to create and maintain large-scale asset management systems [01:26:00].
  • Full-Featured UIs It supports full-featured user interfaces through modules like PySide and Qt for Python [01:42:00].

Key Use Cases in Unreal Editor

Python in the Unreal Editor can be used to:

  • Construct larger-scale asset management pipelines or workflows that link the Unreal Editor to other 3D applications [02:31:00].
  • Automate time-consuming asset management tasks like generating level of details (LODs) or static meshes, though some of this is now handled by Nanite in Unreal Engine 5 [02:39:00].
  • Procedurally lay out content and control the Unreal Editor from custom user interfaces created in Python [03:00:00].

Enabling Python Support

To use Python in Unreal Editor, the “Python Editor Script Plugin” must be enabled [03:43:00]. This plugin includes an embedded version of Python 3.9.7, meaning a separate Python installation is not required on the computer [03:36:00].

Running Python Scripts

Python scripts can be executed in several ways within the Unreal Editor:

Python Console and Output Log

The Unreal Editor’s console input bar can be switched to accept Python code instead of Unreal console commands by pressing the tilde (~) key [08:14:00].

  • Individual lines of Python code can be executed immediately, similar to an interactive Python command line [08:40:00].
  • Multiple lines can be entered by using Shift+Enter to separate lines or by pasting a multi-line block [08:56:00].
  • Python script files can be executed by typing their file name into the console, optionally including command-line arguments [09:08:00]. The pi command can also be used in the normal console to run the rest of the line as Python code [09:27:00].

From the Command Line

Python scripts can be specified in the command line arguments when launching the Unreal Editor. The editor will shut down immediately after running the script [03:05:00].

  • Full Editor Launch: The full Unreal Editor launches, loads the project and default level, and then runs the script. This is suitable for scripts interacting with project content or levels [03:13:00].
  • Headless Mode (Commandlet): This approach is faster and suitable for scripts that can run without a full UI. It can be trickier to load levels or assets [03:47:00].

Startup Scripts

The Unreal Editor can be configured to automatically run Python scripts on startup.

  • init_unreal.py: If a script named init_unreal.py is detected in any configured Python paths (e.g., in the Content/Python subfolder of a project or plugin), it runs automatically upon editor launch [04:51:00, 01:10:07]. This is useful for project- or plugin-specific initialization code [04:07:00].
  • Project Settings: Any number of Python scripts can be specified in the project settings to run every time that specific project is opened [04:48:00]. These scripts run after the default startup level is fully loaded [04:52:00].

From Editor-Only Blueprints

The Python Editor Script Plugin exposes new nodes in the Blueprint Visual Scripting system to run Python code snippets [04:39:00]. These Python execution nodes are only available in editor-only Blueprint classes, such as Editor Utility Widgets and Editor Utility Blueprints [04:47:00, 04:50:00].

Python Environment

Unreal Engine’s embedded Python interpreter runs in isolated mode by default [01:43:00].

  • sys.path: The Unreal Editor automatically adds several paths to Python’s sys.path variable, including the Content/Python subfolder within the project [01:08:02].
  • Additional Paths: Users can add custom paths to the Python environment via project settings, allowing the import of external Python modules [01:12:00].

Unreal Python API (unreal Module)

The unreal module, exposed by the Python Editor Script Plugin, provides a wide range of classes and functions to interact with the Unreal Editor, project assets, and level content [01:17:01].

  • It exposes nearly everything available from C++ to Blueprints within the editor environment [01:43:00].
  • As new plugins are enabled, anything they expose to Blueprints also becomes available in Python [01:55:00].
  • Data Type Conversion: Python lists, sets, and dictionaries are automatically converted to Unreal’s equivalent UArray, USet, or UMap types [02:24:00, 02:37:00].
  • Inheritance Hierarchy: Python classes maintain the same inheritance hierarchy as their C++ and Blueprint counterparts [02:40:00].
  • Naming Conventions: The API balances C++ and Python naming conventions. Classes and objects have the same names as in Blueprints. Properties are automatically exposed as lowercase snake_case, and enums as capital snake_case [02:49:00].

Best Practices

  • Working with Assets: Always use functions from the unreal module for asset operations (e.g., moving files, asset management) instead of Python’s built-in file management modules. This ensures Unreal’s internal asset management is correctly updated [01:36:58].
  • Changing Editor Properties: Use Python to access objects and programmatically set their configuration properties, such as static mesh actor properties (e.g., damageable, hidden in game) [01:37:25]. It’s recommended to use functions like set_editor_property instead of direct assignment [01:38:26].
  • Logging and Feedback: Use unreal.log, unreal.log_warning, and unreal.log_error for outputting messages to the log [01:38:58].
  • Supporting Undo and Redo: Operations that modify the editor state can be wrapped in unreal.ScopedEditorTransaction to ensure they are part of the undo/redo history [01:39:52].
  • Process Dialogues for Slow Operations: For scripts that process many assets or actors and might take time, use unreal.ScopedSlowTask to display progress bars, preventing the editor from appearing frozen [01:44:43].

Conclusion

Python provides a powerful and flexible way to automate tasks within the Unreal Editor. It enables complex workflows, especially for content pipelines involving generative AI models or movie creation, where the final product is images or sequences rather than a game executable [01:46:17]. Future possibilities include integrating Python-based deep learning frameworks like PyTorch to modify or generate content directly within the editor [01:47:20].

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