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An example of an ISP violation occurs when a single interface forces different classes to implement methods they do not need. A classic example is a "multi-function printer" device.

---

### A "fat" interface - an ISP violation

```python
class IMultiFunctionDevice:
    def print(self, document):
        pass

def scan(self, document):
        pass

def fax(self, document):
        pass
```

### The problem

Any class that implements this interface **must** support all three methods, even if it only needs one or two of them.

---

### An implementation that violates ISP

```python
class SimplePrinter(IMultiFunctionDevice):
    def print(self, document):
        print("Printing document")

def scan(self, document):
        raise NotImplementedError("This printer cannot scan")

def fax(self, document):
        raise NotImplementedError("This printer cannot send faxes")
```

---

### Why this is an ISP violation:

1. **The class is forced to implement methods it does not need**
SimplePrinter can neither scan nor send faxes, but the interface forces it to have these methods.
2. **Unnecessary dependencies**
A client that only needs printing now depends on an interface containing scan and fax methods.
3. **Changing the interface breaks the system**
If a new method is added, for example `copy()`, every implementation has to be changed, even those that do not need copying.
4. **Empty and "harmful" methods**
The `scan()` and `fax()` methods in the class are essentially useless stubs and lead to errors when called.

---

### Summary

IMultiFunctionDevice is a typical "fat" interface.
SimplePrinter violates ISP because it is forced to support functionality it does not need, which leads to a fragile and inflexible design.

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