TouchDesigner Tutorial: Essential Python Expressions

This tutorial covers essential Python expressions in TouchDesigner, teaching you how to use dynamic expressions for parameter control and animation.

Getting Started with Python in TouchDesigner

If you’re already familiar with Python, Derivative recommends checking out the User Guide’s Python category, specifically the Quick Start Tutorial and Introduction to Python in TouchDesigner. For beginners, this tutorial covers the most common expressions you’ll use.

Time-Based Expressions

absTime.frame

The absTime.frame expression returns the absolute amount of time that has elapsed since TouchDesigner started running, expressed in frames.

Example: Add a Geometry component and use absTime.frame in a rotation parameter to create continuous animation.

Mathematical operations: You can perform math directly in parameter fields:

• absTime.frame * 0.25 - Slow down the animation
• absTime.frame * 2 - Speed up the animation

absTime.seconds

Similar to absTime.frame, but returns time in seconds instead of frames.

Example: Add a Constant CHOP with a Trail CHOP connected to visualize the value over time.

Using Modulus for Looping

The modulus operator (%) creates repeating cycles:

absTime.seconds % 2

This expression counts from 0 to 2, then resets back to 0, creating a simple ramp that loops every 2 seconds. This is incredibly useful for building cyclical animations and effects.

Path and Parent Expressions

parent.name

Returns the name of the parent operator.

Example: Inside a Container, add a Text component and use parent.name in the text parameter. If you rename the parent container, the text automatically updates.

parent (Full Path)

Using parent without .name returns the complete path to the parent operator.

Example: parent might return /project1/container1/myGreatComp3

This matches the address shown in the pane bar, giving you the full path to the operator’s location.

parent(n) - Accessing Ancestors

You can access grandparents and further ancestors by passing a number:

• parent or parent(1) - Returns the immediate parent
• parent(2) - Returns the grandparent
• parent(2).name - Returns just the grandparent’s name

parent.digits

Returns only the numeric portion of the parent’s name as an integer.

Example: If the parent is named myGreatComp6, parent.digits returns 6.

The TDU Module

The tdu module provides utility functions for common operations in TouchDesigner.

tdu.digits()

Extracts numeric values from any string:

tdu.digits("helloWorld10")  # Returns 10
tdu.digits("myComp19")      # Returns 19

This is extremely useful when extracting numeric values from strings or paths, a common operation when building dynamic systems.

Summary

These essential Python expressions form the foundation for dynamic parameter control in TouchDesigner:

Expression	Returns
absTime.frame	Elapsed time in frames
absTime.seconds	Elapsed time in seconds
value % n	Value cycling from 0 to n
parent.name	Parent operator’s name
parent	Parent operator’s full path
parent(n)	Ancestor n levels up
parent.digits	Numeric portion of parent’s name
tdu.digits(string)	Numeric portion of any string

These expressions enable you to create dynamic, responsive projects where parameters automatically update based on time, hierarchy, and other factors.

absTime.seconds % 2

tdu.digits("helloWorld10")  # 返回 10
tdu.digits("myComp19")      # 返回 19