When is Layer.build() invoked in source code in keras?

Keras is a popular open-source deep learning library written in Python. One of the key components of Keras is the Layer class, which represents a neural network layer. The build() method is a crucial part of the Layer class, as it is responsible for creating the layer’s weights and biases.

The build() method in Keras is invoked when the layer is first used in the network. It is called during the first call of the layer’s __call__() method. This allows the layer to lazily create its weights and biases based on the shape of the input it receives.

When the build() method is called, Keras initializes the layer’s weights using the input shape and the layer’s configuration. This process is important for ensuring that the layer’s parameters match the input data and that the network can be properly trained.

It’s worth noting that the build() method is not executed when the layer is defined or added to the model. Instead, it is deferred until the layer is used for the first time, making it a flexible and efficient way to handle layer initialization in Keras.

Overall, the build() method in Keras is invoked in the source code when a layer is first used in the network, allowing the layer to lazily create its weights and biases based on the input it receives. This approach provides flexibility and efficiency in handling layer initialization in Keras.