Destructors are one of the [special methods](ClassSpecialMethods) of a class.
Destructors are called when an object is garbage collected. `__del__` is a [special name](https://docs.python.org/3/reference/datamodel.html#specialnames). `__del__` called when the instance is about to be destroyed.
This needn't be when an object loses its last reference, or when `del` is called on it.
```python
class A:
  def __init__(self,fn):
    self.fn = fn
    self.file = open(fn)
  def __del__(self):
    print(f"Closing {self.fn}")
    self.file.close()
```