Python: How to check that del instruction called?

Question

I'd like to test function:

#foo_module.py
def foo(*args, **kwargs):
   bar = SomeClass(*args, **kwargs)
   # actions with bar
   del bar

I chose to test the mock library. My test looks like:

@mock.patch('path.to.foo_module.SomeClass')
def test_foo(self, mock_class):
    foo()
    mock_class.assert_called_once_with()

But how I can check that 'del bar' executed? Call of mock_class.return_value.__del__ raises AttributeError.

UPD: Sorry but I didn't mention that SomeClass is django.contrib.gis.gdal.datasource.DataSource. DataSource has overridden __del__ method:

def __del__(self):
    "Destroys this DataStructure object."
    if self._ptr and capi:
        capi.destroy_ds(self._ptr)

In this case del bar have effect outside the function. So I simple should to mock capi and check capi.destroy_ds.called.

How about compare the scope's variables(thing likes `locals` or `globals`) between the function call. — LittleQ, Jul 28 '15 at 10:32
@DanielRoseman, I want check if function works as supposed. Why I shouldn't test this? — ikoverdyaev, Jul 28 '15 at 13:04
Because all `del` does is remove the locally-assigned name inside the function. It does not have any effect at all outside the function. So the test cannot possibly have access to that, and shouldn't care. You can only test things that have effects. — Daniel Roseman, Jul 28 '15 at 13:35

score -1 · Answer 1 · answered Jul 28 '15 at 10:19

Check the dir() result to see that object is still there:

>>> dir()
['__builtins__', '__doc__', '__name__', '__package__']
>>> a=10
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'a']
>>> del a
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__']

For this script:

def f() :
    a = 10
    print dir()
    del a
    print dir()
    objLst = dir()
    if 'a' not in objLst :
        print 'Object deleted'

f()

you get the output:

['a']
[]
Object deleted

Python: How to check that del instruction called?

1 Answers1