Anyways when debuging my code I found statement that basically subtracted `boolean` from `float`.

Then I tried following in python console: 

```
>>> 15.0 - True 
14.0
>>> 15.0 - False
15.0

```

Can anyone explain to me: 

* Why subtracting booleans from numeric types is legal (the docs only state that you can do `and`, `not` and `or` on boolean values: <http://docs.python.org/3/library/stdtypes.html#boolean-operations-and-or-not>)
* Has this any practical use?