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An SRP violation occurs when a single class takes on different responsibilities that belong to different layers or aspects of the system. Example:

## Example of a class that violates SRP

```python
class OrderService:
    def create_order(self, order_data):
        # business logic for creating an order
        self._validate(order_data)
        self._save_to_db(order_data)

# send a notification to the customer
        self._send_email(order_data["email"])

# write to the log file
        with open("orders.log", "a") as f:
            f.write(f"Order created: {order_data}\n")

def _validate(self, data):
        ...

def _save_to_db(self, data):
        ...

def _send_email(self, email):
        ...
```

## Breaking down the violation

1. **Business logic**
The methods `create_order`, `_validate`, `_save_to_db` belong to the "orders" domain.
2. **Notifications**
The `_send_email` method belongs to communications - a different responsibility.
3. **Logging**
Writing to `orders.log` belongs to infrastructure - a third responsibility.

As a result, the class has **three reasons to change**:

- the order-creation process changes → the class must be changed;
- the email-notification format changes → the same class must be changed;
- logging requirements change → the same class must be changed again.

This is a direct SRP violation.

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