Parameter expressions#

Overview#

Almost any parameter on Lifeblood’s nodes can have a simple value that will be just always constant, or an expression.

A parameter expression is a piece of code that will be evaluated any time a task being processed tries to get node’s parameter value.

Currently only Python expressions are supported.

A Python Expression#

A python parameter expression can be any python expression. Returned value will be casted to appropriate parameter value type if possible. If not possible - an exception will be thrown and task evaluating that expression will be marked as Errored.

the following modules are imported into the context of expression evaluation:

os
pathlib
contents of math (as if from math import * was performed)

The following names are defined in the context of evaluation:

task - the task being processed
node - the node that owns this parameter
config - this node’s configuration at scheduler’s side

task#

represents task being processed, the following methods available:

__getitem__ - retrieve any task’s attribute: you can access task attributes with simple syntax: task['attr_name']

for example, task['file'] task['frames'][0]
get(attr_name, default=None) - same, but with optional default on attr_name being not found: together with previous method they provide access interface similar to that of a dict

task.get('preferred_filename', 'untitled.mov')
id: task internal id
task.parent_id: parent task id if this task has a parent, otherwise None
task.name: name of this task (if task was created internally - name may ne None)

node#

__getitem__ - retrieve any node’s parameter value: you can access other node’s parameters with simple syntax: node['param_name']

for example, node['hip path'] task['driver path']
name: name of the node
label: label of the node type, label is used in tab node creation menu

config#

__getitem__/get - retrieve any task’s attribute: get value from this node type’s config on scheduler side.

scheduler has a special config file for nodes’ custom values

Config location /scheduler/nodes/config.toml (read more here: custom node type configuration)