# nodes

Python API: `luxonis_train.nodes`

The building blocks of a model graph.

A node is one computational unit of the model. An entry in the `model.nodes` section of the config names a node class. The
`inputs` field of the entry lists the nodes that feed the node. The `input_sources` field lists the loader outputs that feed it.
Every node inherits
[BaseNode](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/base_node.md).

 * [luxonis_train.nodes.backbones](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/backbones.md)
   holds the backbones. A backbone turns an image into feature maps.
 * [luxonis_train.nodes.necks](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/necks.md)
   holds the necks. A neck fuses the feature maps of a backbone.
 * [luxonis_train.nodes.heads](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/heads.md)
   holds the heads. A head turns features into predictions for a task.
 * [luxonis_train.nodes.blocks](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/blocks.md)
   holds the layers that several nodes share.

A head carries a task. The task decides which losses, metrics, and visualizers can attach to the head. The docstring of each head
lists them.

## Child Pages

 * [backbones](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/backbones.md)
 * [blocks](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/blocks.md)
 * [heads](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/heads.md)
 * [necks](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/necks.md)
 * [base_node](https://docs.luxonis.com/software-v3/ai-inference/model-source/training/luxonis-train/luxonis-train-api-reference/nodes/base_node.md)