'ExponentialLR' object has no attribute 'zero_grad'

The error message you are seeing suggests that you are trying to call the `zero_grad()` method on an instance of the `ExponentialLR` class, which does not have this method.

`zero_grad()` is a method defined in the `torch.optim.Optimizer` class, which is used to set the gradients of all the parameters to zero before backpropagation.

You should make sure that you are calling `zero_grad()` on an instance of the `Optimizer` class, not the `ExponentialLR` class. Here is an example of how to use `zero_grad()` properly:

import torch
import torch.optim as optim

optimizer = optim.SGD(model.parameters(), lr=0.1)
scheduler = optim.lr_scheduler.ExponentialLR(optimizer, gamma=0.9)

# perform a forward pass and compute loss
loss.backward()

# set gradients to zero
optimizer.zero_grad()

# perform backpropagation
optimizer.step()

# update learning rate
scheduler.step()

In this example, `zero_grad()` is called on the `optimizer` instance, not the `scheduler` instance.