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# Migrating your code to 🤗 Accelerate
This tutorial will detail how to easily convert existing PyTorch code to use 🤗 Accelerate!
You'll see that by just changing a few lines of code, 🤗 Accelerate can perform its magic and get you on
your way towards running your code on distributed systems with ease!
## The base training loop
To begin, write out a very basic PyTorch training loop.
<Tip>
We are under the presumption that `training_dataloader`, `model`, `optimizer`, `scheduler`, and `loss_function` have been defined beforehand.
</Tip>
```python
device = "cuda"
model.to(device)
for batch in training_dataloader:
optimizer.zero_grad()
inputs, targets = batch
inputs = inputs.to(device)
targets = targets.to(device)
outputs = model(inputs)
loss = loss_function(outputs, targets)
loss.backward()
optimizer.step()
scheduler.step()
```
## Add in 🤗 Accelerate
To start using 🤗 Accelerate, first import and create an [`Accelerator`] instance:
```python
from accelerate import Accelerator
accelerator = Accelerator()
```
[`Accelerator`] is the main force behind utilizing all the possible options for distributed training!
### Setting the right device
The [`Accelerator`] class knows the right device to move any PyTorch object to at any time, so you should
change the definition of `device` to come from [`Accelerator`]:
```diff
- device = 'cuda'
+ device = accelerator.device
model.to(device)
```
### Preparing your objects
Next you need to pass all of the important objects related to training into [`~Accelerator.prepare`]. 🤗 Accelerate will
make sure everything is setup in the current environment for you to start training:
```
model, optimizer, training_dataloader, scheduler = accelerator.prepare(
model, optimizer, training_dataloader, scheduler
)
```
These objects are returned in the same order they were sent in with. By default when using `device_placement=True`, all of the objects that can be sent to the right device will be.
If you need to work with data that isn't passed to [~Accelerator.prepare] but should be on the active device, you should pass in the `device` you made earlier.
<Tip warning={true}>
Accelerate will only prepare objects that inherit from their respective PyTorch classes (such as `torch.optim.Optimizer`).
</Tip>
### Modifying the training loop
Finally, three lines of code need to be changed in the training loop. 🤗 Accelerate's DataLoader classes will automatically handle the device placement by default,
and [`~Accelerator.backward`] should be used for performing the backward pass:
```diff
- inputs = inputs.to(device)
- targets = targets.to(device)
outputs = model(inputs)
loss = loss_function(outputs, targets)
- loss.backward()
+ accelerator.backward(loss)
```
With that, your training loop is now ready to use 🤗 Accelerate!
## The finished code
Below is the final version of the converted code:
```python
from accelerate import Accelerator
accelerator = Accelerator()
model, optimizer, training_dataloader, scheduler = accelerator.prepare(
model, optimizer, training_dataloader, scheduler
)
for batch in training_dataloader:
optimizer.zero_grad()
inputs, targets = batch
outputs = model(inputs)
loss = loss_function(outputs, targets)
accelerator.backward(loss)
optimizer.step()
scheduler.step()
```
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