boolean-functor.py

class BooleanFunctor:
    """
    A neat trick: this can be used in conditions, where it returns the value of b,
    or as a decorator, where it returns the decorated function if b, or a lambda returning
    falseValue otherwise.

    >>> if BooleanFunctor(cond):
    ...  # only if cond is true
    ...  pass

    >>> @BooleanFunctor(cond)
    ... def foo():
    ...   pass
    >>> # If cond, v would equal foo(), otherwise it'd be falseValue
    >>> v = foo()
    """
    
    def __init__(self, b, falseValue=False):
        self.b = b
        self.falseValue = falseValue
    
    def __nonzero__(self):
        return self.b
    
    def __call__(self, f):
        return f if self.b else lambda *a, **k: falseValue