Boolean value of objects in Python

by

In Python < 3.0 :

You have to use __nonzero__ to achieve what you want. It’s a method that is called automatically by Python when evaluating an object in a boolean context. It must return a boolean that will be used as the value to evaluate.

E.G :

class Foo(object):

    def __init__(self, bar) :
        self.bar = bar

    def __nonzero__(self) :
        return self.bar % 2 == 0

if __name__ == "__main__":
     if (Foo(2)) : print "yess !"

In Python => 3.0 :

Same thing, except the method has been renamed to the much more obvious __bool__.

More Related Contents:

  1. Why does “a == x or y or z” always evaluate to True?
  2. Parsing boolean values with argparse
  3. Converting from a string to boolean in Python?
  4. Why is bool a subclass of int?
  5. if x:, vs if x == True, vs if x is True
  6. How can I map True/False to 1/0 in a Pandas DataFrame?
  7. Comparing boolean and int using isinstance
  8. Python’s in (__contains__) operator returns a bool whose value is neither True nor False
  9. SQLAlchemy: unexpected results when using `and` and `or`
  10. What is the motivation for the “or” operator to not return a bool?
  11. Python AND operator on two boolean lists – how?
  12. Why is ‘True == not False’ a SyntaxError?
  13. overriding bool() for custom class [duplicate]
  14. Evaluation of boolean expressions in Python
  15. Boolean identity == True vs is True
  16. Python: False vs 0
  17. Why does “a == x or y or z” always evaluate to True? How can I compare “a” to all of those?
  18. double equals vs is in python [duplicate]
  19. Python evaluates 0 as False
  20. Empty list boolean value
  21. Counting the number of True Booleans in a Python List
  22. python tilde unary operator as negation numpy bool array
  23. Convert Pandas series containing string to boolean
  24. User input boolean in python
  25. How do I use a Boolean in Python?
  26. Convert True/False value read from file to boolean
  27. Why does bool(xml.etree.ElementTree.Element) evaluate to False?
  28. What does an ‘x = y or z’ assignment do in Python?
  29. Select elements of numpy array via boolean mask array
  30. Difference between “if x” and “if x is not None”

Leave a Comment