Библиотека Python разработчика(@BookPython). In Python, each value has a boolean value. It is implicitly cast when you use if, bool, not etc. Fa

In Python, each value has a boolean value. It is implicitly cast when you use if, bool, not etc. False objects are None, False, 0 of any type, and empty collections: "", [], {} etc., including custom collections with the __len__ method as long as __len__ returns 0. You can also define custom truth value testing for your objects, the __bool__ magic method is there for this:

class Rectangle:
    def __init__(self, width, height):
        self._w = width
        self._h = height
        
    def __bool__(self):
        return bool(self._w and self._h)

In : bool(Rectangle(2, 3))
Out: True
In : bool(Rectangle(2, 0))
Out: False
In : bool(Rectangle(0, 2))
Out: False

Mind, that __bool__ is called __nonzero__ in Python 2.