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transformer_spec.py
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transformer_spec.py
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"""Declares specification of the Transformer model."""
import numpy as np
from ctranslate2.specs import attention_spec
from ctranslate2.specs import common_spec
from ctranslate2.specs import model_spec
class TransformerSpec(model_spec.ModelSpec):
"""Describes a Transformer model.
The specification is invariant to hidden dimensions but requires to
explicitly set the number of layers and attention heads.
"""
def __init__(self, num_layers, num_heads):
self.num_heads = np.dtype("int8").type(num_heads)
self.encoder = TransformerEncoderSpec(num_layers)
self.decoder = TransformerDecoderSpec(num_layers)
@property
def revision(self):
return 3
@property
def source_vocabulary_size(self):
return self.encoder.embeddings.weight.shape[0]
@property
def target_vocabulary_size(self):
return self.decoder.embeddings.weight.shape[0]
class TransformerEncoderSpec(model_spec.LayerSpec):
def __init__(self, num_layers):
self.embeddings = common_spec.EmbeddingsSpec()
self.position_encodings = PositionEncoderSpec()
self.layer_norm = common_spec.LayerNormSpec()
self.layer = [TransformerEncoderLayerSpec() for _ in range(num_layers)]
class TransformerDecoderSpec(model_spec.LayerSpec):
def __init__(self, num_layers):
self.embeddings = common_spec.EmbeddingsSpec()
self.position_encodings = PositionEncoderSpec()
self.layer_norm = common_spec.LayerNormSpec()
self.projection = common_spec.LinearSpec()
self.layer = [
TransformerDecoderLayerSpec() for _ in range(num_layers)]
class TransformerEncoderLayerSpec(model_spec.LayerSpec):
def __init__(self):
self.self_attention = attention_spec.MultiHeadAttentionSpec(self_attention=True)
self.ffn = FeedForwardSpec()
class TransformerDecoderLayerSpec(model_spec.LayerSpec):
def __init__(self):
self.self_attention = attention_spec.MultiHeadAttentionSpec(self_attention=True)
self.attention = attention_spec.MultiHeadAttentionSpec()
self.ffn = FeedForwardSpec()
class FeedForwardSpec(model_spec.LayerSpec):
def __init__(self):
self.layer_norm = common_spec.LayerNormSpec()
self.linear_0 = common_spec.LinearSpec()
self.linear_1 = common_spec.LinearSpec()
class PositionEncoderSpec(model_spec.LayerSpec):
def __init__(self):
self.encodings = model_spec.OPTIONAL