"""
Lazily-evaluated property pattern in Python.
https://en.wikipedia.org/wiki/Lazy_evaluation
References:
bottle
https://github.com/bottlepy/bottle/blob/cafc15419cbb4a6cb748e6ecdccf92893bb25ce5/bottle.py#L270
django
https://github.com/django/django/blob/ffd18732f3ee9e6f0374aff9ccf350d85187fac2/django/utils/functional.py#L19
pip
https://github.com/pypa/pip/blob/cb75cca785629e15efb46c35903827b3eae13481/pip/utils/__init__.py#L821
pyramimd
https://github.com/Pylons/pyramid/blob/7909e9503cdfc6f6e84d2c7ace1d3c03ca1d8b73/pyramid/decorator.py#L4
werkzeug
https://github.com/pallets/werkzeug/blob/5a2bf35441006d832ab1ed5a31963cbc366c99ac/werkzeug/utils.py#L35
"""
class (object):
def __init__(self, function):
self.function = function
functools.update_wrapper(self, function)
def __get__(self, obj, type_):
if obj is None:
return self
val = self.function(obj)
obj.__dict__[self.function.__name__] = val
return val
class Person(object):
def __init__(self, name, occupation):
self.name = name
self.occupation = occupation
def relatives(self):
relatives = "Many relatives."
return relatives
def main():
Jhon = Person('Jhon', 'Coder')
print("Name: {0} Occupation: {1}".format(Jhon.name, Jhon.occupation))
print("Before we access `relatives`:")
print(Jhon.__dict__)
print("Jhon's relatives: {0}".format(Jhon.relatives))
print("After we've accessed `relatives`:")
print(Jhon.__dict__)