Houdini 18.0 Nodes TOP nodes

Python Partitioner TOP node

Partitions work items using a Python script

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This node can be used to write custom partitioner logic using the Python API. PDG will call the script hooks on this node to partition upstream work items. The Partitioner node API reference has a detailed explanation for each of the callback functions that you can implement.

For use cases that can expressed as a single line Python or HScript expression, the Partition by Expression is a simpler alternative.

Parameters

Save to Python Script

Saves the callbacks defined on this node to a Python script, which can be imported and registered with PDG. The parameter template associated with the node is also saved and embedded into the Python script. After saving the script is automatically imported and the node type is made available in the TAB menu.

Save to Digital Asset

Saves the callbacks defined on this node to a standalone Houdini Digital asset. The callbacks are stored inside the .hda itself and are registered with PDG as an embedded PDG node type.

Use Dynamic Partitioning

When on, the partitioner waits for all input work items to be generated before partitioning them. If the input work items are dynamic, then the partitioner has to wait for and depends on the parent(s) of those items.

Merge Input Attributes

When on, the partitioner merges the attributes of the work items in each partition and exports them to the partition itself.

onPartition Callback

This script is run in order to partition the upstream items.

If this is a static partitioner it is run once during the static cook with the full list of upstream static items as input. If this is a dynamic partitioner it is run once during the cook based on the value of the Partition When parameter.

Several variables are available in the script:

self

Refers to the underlying PDG node associated with the TOP node. Note that this is different than TOP node itself, which is a standard Houdini operator.

Spare parameters added to the TOP node’s parameter interface will automatically be added to the PDG node.

partition_holder

The partition holder used to add work items to partitions. Partitions will be committed to the node once the script completes. If there are any errors during the script, the contents of the partition holder is discarded.

work_items

The list of work items to partition.

Advanced

These are advanced parameters that provide finer control over the behavior of the partitioner.

Auto Remove Stale Dependencies

When on, the partitioner removes old dependencies when recooking the node if the partitioning scheme changes as a result of the cook.

Force Re-Evaluation on Cook

When on, forces the partitioner to re-evaluate the partitioning scheme even if all of the work items are already cooked and no new work items have been added.

Dirtying Mode

Determines when a partition is dirtied and the effects on child items when that occurs. This is particularity useful for working around some of the limitations of using dynamic partitioning.

Standard

A given partition is dirtied when any of the work items in the partition are dirtied. In the case of dynamic partitioning, if any ancestor of a dynamic work item in a partition is dirtied, then all partitions are dirtied.

When a partition is dirtied, all of its children are deleted.

Non-destructive

The same dirtying behavior as Standard, except when a partition is dirtied, its children are dirtied instead of deleted.

Mapping Standard

A given partition is only dirtied if an item in the partition is dirtied or if the partition’s contents change as a result of a recook. When the partition is dirtied, any child work items are deleted.

Mapping Non-destructive

The same dirtying behavior as Mapping Standard, except when a partition is dirtied, its children are dirtied instead of deleted.

Split by Attribute

When on, the node splits input work items by the specified attribute before partitioning them. The partitioning logic is evaluated on the list of work items for each distinct attribute value. Work items with different attribute values are always put into different partitions.

Missing Attribute

Determines how the node handles work items that are missing the split attribute.

This parameter is only available when Split by Attribute is on.

Ignore Work Item

Work items that are missing the split attribute are not put into any of the partitions.

Partitioner Defines Behavior

The partitioner node determines what happens to work items that are missing the split attribute. Typically a partitioner node that exposes this option will rename this menu entry to describe the actual operation it performs.

Add Work Item to All Partitions

Work items that are missing the split attribute are put into all of the partitions.

Sort Contents By

Determines the order that work items are sorted in when accessing the partitions on this node. This also affects the sort order of output files on the partition.

None

No sorting is applied. The work items in the partition are handled in no particular order.

Work Item Index

Work items in the partition are sorted based on their index.

Input Node Order

Work items in the partition are sorted based on the order of input nodes wired into this node. If two work items are from the same input, they are then sorted by index.

Attribute

Work items in the partition are sorted based on the attribute specified in the Sort Attribute field parameter.

Sort Direction

Determines whether the work items in this node’s partitions are sorted in ascending or descending order.

Sort Attribute

Specifies the name of the attribute to sort by.

This parameter is only available when Sort Contents By is set to Attribute.

Partition When

Determines when the partitioning step is performed on the input work items.

This parameter is only available when Use Dynamic Partitioning is on.

Input Items Are Generated

Inputs are partitioned once all of them have been generated.

Input Items Are Cooked

Inputs are partitioned once all of them are cooked. This is required when the partitioning scheme is based on the results of the work items' execution.

This makes this partitioner behave like a Wait for All node except that it may create multiple partitions.

Partition Target

Specifies the target TOP node for the partition. The partition scheme is applied to the work items in the target TOP node instead of this node’s input work items. The target TOP node must be a processor in the same graph above this node, and there cannot be any other mappers or partitioners between this node and the target.

This parameter is only available when Use Dynamic Partitioning is on.

Examples

example_top_pythonpartitioner Example for Python Partitioner TOP node

This example demonstrates how to use the Python Partitioner node in PDG/TOPs.

See also

TOP nodes