supported_operations = ["__add__", "__sub__", "__mul__", "__floordiv__", "__mod__", "__divmod__", "__pow__", "__lshift__", "__rshift__", "__and__", "__xor__", "__or__", "__pow__", "__div__", "__truediv__", "__div__", "__radd__", "__rsub__", "__rmul__", "__rdiv__", "__rtruediv__", "__rfloordiv__", "__rmod__", "__rdivmod__", "__rpow__", "__rlshift__", "__rrshift__", "__rand__", "__rxor__", "__ror__", "__sub__", "__rpow__", "__radd__", "__neg__", "__pos__", "__abs__", "__complex__", "__long__", "__float__", "__oct__", "__hex__", "__index__", "__len__"] class Wrapper(object): """Wrap a value so that it will be lazy-evaluated. `wrapper.value` returns the current value (you can also use c(wrapper)).""" def __init__(self, target, attribute=None, arguments=None): self.target = target self.attribute = attribute self.arguments = arguments if attribute is not None and arguments is not None: raise TypeError @property def value(self): if self.attribute is None and self.arguments is None: return self.target if self.attribute is not None: return getattr(c(self.target), self.attribute) if self.arguments is not None: return c(self.target)(*map(c, self.arguments)) @value.setter def value(self, new_target): self.target = new_target def __getattr__(self, name): return Wrapper(self, attribute=name) def __call__(self, *args): return Wrapper(self, arguments=args) def __repr__(self): return str(self) def __str__(self): if self.attribute is None and self.arguments is None: return "w(" + str(self.target) + ")" if self.attribute is not None: return "w(" + str(self.target) + "." + str(self.attribute) + ")" if self.arguments is not None: return "w(" + str(self.target) + "(" + ",".join(map(str, self.arguments)) + ")" def pass_through(operation): return lambda self, *others: Wrapper(Wrapper(self, attribute=operation), arguments=others) for operation in supported_operations: setattr(Wrapper, operation, pass_through(operation)) def c(g): """Get the current value of a wrapper or bare variable.""" if isinstance(g, Wrapper): return g.value else: return g def wrap(v): """Wrap a variable, or just return it if it's already wrapped.""" if isinstance(v, Wrapper): return v else: return Wrapper(v) if __name__ == "__main__": foo, bar, baz = wrap(1), wrap(2), wrap(3) print("foo, bar, and baz are the wrapped values 1, 2, and 3.") boop = foo + bar*baz print("boop is set to foo + bar*baz: %s" % (boop, )) print("And we can fetch the value of that computation easily as boop.value: %s" % (boop.value, )) print print("We can change the value of foo:") print(">>> foo.value = 5") foo.value = 5 print("And now, when we fetch the value of boop, it is adjusted accordingly:") print(">>> boop.value => %s" % (boop.value,)) print print("There is also a shorthand for evaluating a glomp: c(boop) => %s" % (c(boop), ))