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import torch
import torch.nn as nn

from networks.base_model import BaseModel
from networks.resnet import resnet50


class Trainer(BaseModel):
    def name(self):
        return 'Trainer'

    def __init__(self, opt):
        super(Trainer, self).__init__(opt)

        if self.isTrain and not opt.continue_train:
            self.model = resnet50(pretrained=True)
            self.model.fc = nn.Linear(2048, 1)
            torch.nn.init.normal_(self.model.fc.weight.data, 0.0, opt.init_gain)

        if not self.isTrain or opt.continue_train:
            self.model = resnet50(num_classes=1)

        if self.isTrain:
            self.loss_fn = nn.BCEWithLogitsLoss()
            # initialize optimizers
            if opt.optim == 'adam':
                self.optimizer = torch.optim.Adam(
                    self.model.parameters(), lr=opt.lr, betas=(opt.beta1, 0.999)
                )
            elif opt.optim == 'sgd':
                self.optimizer = torch.optim.SGD(
                    self.model.parameters(), lr=opt.lr, momentum=0.0, weight_decay=0
                )
            else:
                raise ValueError('optim should be [adam, sgd]')

        if not self.isTrain or opt.continue_train:
            self.load_networks(opt.epoch)
        self.model.to(opt.gpu_ids[0])

    def adjust_learning_rate(self, min_lr=1e-6):
        for param_group in self.optimizer.param_groups:
            param_group['lr'] /= 10.0
            if param_group['lr'] < min_lr:
                return False
        return True

    def set_input(self, input):
        self.input = input[0].to(self.device)
        self.label = input[1].to(self.device).float()

    def forward(self):
        self.output = self.model(self.input)

    def get_loss(self):
        return self.loss_fn(self.output.squeeze(1), self.label)

    def optimize_parameters(self):
        self.forward()
        self.loss = self.loss_fn(self.output.squeeze(1), self.label)
        self.optimizer.zero_grad()
        self.loss.backward()
        self.optimizer.step()