PyTorch for Deep Learning Course TypeError problem

I am trying to go through the Pytorch for Deep Learning course. While I am implementing a module and try to train it I get this problem:

TypeError                                 Traceback (most recent call last)
<ipython-input-25-5e18d2675f50> in <module>
----> 1 history1 = fit(5, 0.001, model_1, train_loader, val_loader)

<ipython-input-21-ed68bbaee875> in fit(epochs, lr, model, train_loader, val_loader, opt_func)
      8         for images,_ in train_loader:
      9             print(images.dtype)
---> 10             loss =
     11             print(loss.dtype)
     12             loss.backward()

TypeError: 'bool' object is not callable

And here is my original fit() function code:

def fit(epochs, lr, model, train_loader, val_loader, opt_func=torch.optim.SGD):
    optimizer = opt_func(model_1.parameters(), lr)
    epoch_result = [] #record epoch wise results
    for epoch in range (epochs):
        #trainging phase
        for images,_ in train_loader:
            loss =
        #validation phase
            result = evaluate(model_1, val_loader)
            model_1.epoch_end(epoch, result)
    return epoch_result 

Can anyone explain to me what is the cause of the problem? I don’t understand why suddenly there is a boolean object and actually which object is the error referring to. Thank you in advance~