src/transformers/models/maskformer/modeling_maskformer.py/MaskFormerFPNModel/forward
class MaskFormerFPNModel:    def forward(self, features: List[Tensor]) -> List[Tensor]:
        fpn_features = []
        last_feature = features[-1]
        other_features = features[:-1]
        output = self.stem(last_feature)
        for layer, left in zip(self.layers, other_features[::-1]):
            output = layer(output, left)
            fpn_features.append(output)
        return fpn_features