git » pymisc » master » tree

[master] /

lazy - Decorators and utilities for lazy evaluation in Python
Alberto Bertogli (

class _LazyWrapper:
	"""Lazy wrapper class for the decorator defined below.
	It's closely related so don't use it.

	We don't use a new-style class, otherwise we would have to implement
	stub methods for __getattribute__, __hash__ and lots of others that
	are inherited from object by default. This works too and is simple.
	I'll deal with them when they become mandatory.
	def __init__(self, f, args, kwargs):
		self._override = True
		self._isset = False
		self._value = None
		self._func = f
		self._args = args
		self._kwargs = kwargs
		self._override = False

	def _checkset(self):
		if not self._isset:
			self._override = True
			self._value = self._func(*self._args, **self._kwargs)
			self._isset = True
			self._checkset = lambda: True
			self._override = False

	def __getattr__(self, name):
		if self.__dict__['_override']:
			return self.__dict__[name]
		return self._value.__getattribute__(name)

	def __setattr__(self, name, val):
		if name == '_override' or self._override:
			self.__dict__[name] = val
		setattr(self._value, name, val)

def lazy(f):
	"Lazy evaluation decorator"
	def newf(*args, **kwargs):
		return _LazyWrapper(f, args, kwargs)

	return newf