confused by bindings

[Joshua Macy]

Doing self.count += 1 in the __init__ creates an instance variable.  You 
  have to either refer to it by the explicit class variable name, e.g. 
A.count, or you have to use a mutable type like a list and do e.g. 
self.count[0].  Look at what's in the dictionaries:

 >>> class A:
... 
count = 0
... 
def __init__(self):
... 
	self.count += 1
...
 >>> a = A()
 >>> b = A()
 >>> dir(A)
['__doc__','__init__','__module__','count']
 >>> A.count
0
 >>> A.__dict__['count']
0
 >>> dir(a)
['count']
 >>> a.count
1
 >>> a.__dict__['count']
1
 >>> class B:
... 
count = []
... 
def __init__(self):
... 
	self.count[0] += 1
...
 >>> c = B()
 >>> d = B()
 >>> dir(B)
['__doc__','__init__','__module__','count']
 >>> B.count
[2]
 >>> dir(c)
[]

Does that help any?

Joshua


Sam Falkner wrote:

> Here's what I've found.  I tried four different methods, putting them
> into two modules: work and test.  The four methods:
> 
>     (1) Borg class,
>     (2) class variable, set as self.count,
>     (3) class variable, set as Class.count, and
>     (4) global-to-module variable.
> 
> When I tried this, (1) and (2) failed, (3) and (4) worked.  But, I
> went back and re-applied (3) and (4) to my existing application, and
> they still failed.
> 
> I would have expected all four of these to work, except perhaps (2),
> which I would have expected either to work or to fail with a NameError 
> or somesuch.
> 
> Here are the two modules.  My output is as follows:
> 
> $ ./test.py -v
> testFour (test.WorkTestCase) ... ok
> testOne (test.WorkTestCase) ... FAIL
> testThree (test.WorkTestCase) ... ok
> testTwo (test.WorkTestCase) ... FAIL
> 
> ======================================================================
> FAIL: testOne (test.WorkTestCase)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "./test.py", line 13, in testOne
>     self.failUnlessEqual(len(junk), b.countone)
>   File "/opt/etext/lib/python2.1/unittest.py", line 273, in failUnlessEqual
>     raise self.failureException, (msg or '%s != %s' % (first, second))
> AssertionError: 5 != 1
> ======================================================================
> FAIL: testTwo (test.WorkTestCase)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "./test.py", line 19, in testTwo
>     self.failUnlessEqual(len(junk), work.Two.count)
>   File "/opt/etext/lib/python2.1/unittest.py", line 273, in failUnlessEqual
>     raise self.failureException, (msg or '%s != %s' % (first, second))
> AssertionError: 5 != 0
> ----------------------------------------------------------------------
> Ran 4 tests in 0.003s
> 
> FAILED (failures=2)
> 
> Note that I still can't get *anything* to work in my real application.
> 
> Can anyone explain what's going on?  Or, if this was discussed a month 
> or so ago, can someone tell me the subject line, so I can look it up
> on google?
> 
> Thanks!
> 
> - Sam
> 
> #! /usr/bin/env python
> 
> # work.py module
> 
> class Borg:
>     __shared_state = {}
>     def __init__(self):
>         self.__dict__ = self.__shared_state
>         self.countone = 0
> 
> class One:
>     def __init__(self):
>         borg = Borg()
>         borg.countone += 1
> 
> class Two:
>     count = 0
>     def __init__(self):
>         self.count += 1
> 
> class Three:
>     count = 0
>     def __init__(self):
>         Three.count += 1
> 
> fourcount = 0
> 
> class Four:
>     def __init__(self):
>         global fourcount
>         fourcount += 1
> 
> def work1():
>     junk = []
>     for i in range(5):
>         junk.append(One())
>     return junk
> 
> def work2():
>     junk = []
>     for i in range(5):
>         junk.append(Two())
>     return junk
> 
> def work3():
>     junk = []
>     for i in range(5):
>         junk.append(Three())
>     return junk
> 
> def work4():
>     junk = []
>     for i in range(5):
>         junk.append(Four())
>     return junk
> 
> #! /usr/bin/env python
> 
> # test.py module
> 
> import unittest
> 
> import work
> 
> class WorkTestCase(unittest.TestCase):
>     def testOne(self):
>         b = work.Borg()
>         b.countone = 0
>         junk = work.work1()
>         self.failUnlessEqual(len(junk), b.countone)
> 
>     def testTwo(self):
>         work.Two.count = 0
>         junk = work.work2()
>         self.failUnlessEqual(len(junk), work.Two.count)
> 
>     def testThree(self):
>         work.Three.count = 0
>         junk = work.work3()
>         self.failUnlessEqual(len(junk), work.Three.count)
> 
>     def testFour(self):
>         work.fourcount = 0
>         junk = work.work4()
>         self.failUnlessEqual(len(junk), work.fourcount)
> 
> def buildall():
>     return unittest.makeSuite(WorkTestCase, 'test')
> 
> if __name__ == '__main__':
>     unittest.main('test', 'buildall')
>