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Are Python properties broken?

How can it be that this test case

import unittest

class PropTest(unittest.TestCase):
def test(self):
class C():
val = 'initial val'

def get_p(self):
return self.val

def set_p(self, prop):
if prop == 'legal val':
self.val = prop

prop=property(fget=get_p, fset=set_p)

c=C()
self.assertEqual('initial val', c.prop)

c.prop='legal val'
self.assertEqual('legal val', c.prop)

c.prop='illegal val'
self.assertNotEqual('illegal val', c.prop)


fails as below?

Failure
Traceback (most recent call last):
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/unittest.py", line 279, in run
testMethod()
File "/Users/jacob/aau/admissions_proj/admissions/plain_old_unit_tests.py", line 24, in test
self.assertNotEqual('illegal val', c.prop)
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/unittest.py", line 358, in failIfEqual
(msg or '%r == %r' % (first, second))
AssertionError: 'illegal val' == 'illegal val'


property

Object

1 Answer
1

Your class C does not inherit from object or any other new-style class, so it is an old-style class (and therefore does not support properties). Descriptors are for new-style classes only. To fix, change class C() to class C(object).

C

object

class C()

class C(object)

http://www.python.org/download/releases/2.2.3/descrintro/ provides some details, if you are interested. New-style classes are better in several ways.

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