builtin_property.py

# test builtin property
try:
    property
except:
    print("SKIP")
    raise SystemExit

# create a property object explicitly
property()
property(1, 2, 3)

# use its accessor methods
p = property()
p.getter(1)
p.setter(2)
p.deleter(3)

# basic use as a decorator
class A:
    def __init__(self, x):
        self._x = x

    @property
    def x(self):
        print("x get")
        return self._x

a = A(1)
print(a.x)

try:
    a.x = 2
except AttributeError:
    print("AttributeError")

# explicit use within a class
class B:
    def __init__(self, x):
        self._x = x

    def xget(self):
        print("x get")
        return self._x

    def xset(self, value):
        print("x set")
        self._x = value

    def xdel(self):
        print("x del")

    x = property(xget, xset, xdel)

b = B(3)
print(b.x)
b.x = 4
print(b.x)
del b.x

# full use as a decorator
class C:
    def __init__(self, x):
        self._x = x

    @property
    def x(self):
        print("x get")
        return self._x

    @x.setter
    def x(self, value):
        print("x set")
        self._x = value

    @x.deleter
    def x(self):
        print("x del")

c = C(5)
print(c.x)
c.x = 6
print(c.x)
del c.x

# a property that has no get, set or del
class D:
    prop = property()
d = D()
try:
    d.prop
except AttributeError:
    print('AttributeError')
try:
    d.prop = 1
except AttributeError:
    print('AttributeError')
try:
    del d.prop
except AttributeError:
    print('AttributeError')

# properties take keyword arguments
class E:
    p = property(lambda self: 42, doc="This is truth.")
    # not tested for because the other keyword arguments are not accepted
    # q = property(fget=lambda self: 21, doc="Half the truth.")
print(E().p)

# a property as an instance member should not be delegated to
class F:
    def __init__(self):
        self.prop_member = property()
print(type(F().prop_member))