[TIP] Using Mock to patch an iterator / generator?

[Michael Foord]

On 11/06/2011 10:35, Michael Foord wrote:
> On 10/06/2011 00:08, Andrew Hammond wrote:
>> I have a class that looks like
>>
>> class Foo(object):
>>     def iter(descending=False):
>>         for r in something_iterable:
>>             yield r
>>
>>
> Hey Andrew,
>
> Because of the use of yield, your iter is a generator and not a normal 
> method. Mocking a generator (or any iterable) can be done with the 
> MagicMock (in mock 0.7).
>
> You can then configure the return values using something similar to this:
>
> mock = MagicMock()
>
> values = [1, 2, 3]
> mock.iter.__iter__.side_effect = lambda: values.pop()
>

Actually, this isn't quite correct (my apologies).

Foo.iter *returns* a generator when called. It isn't directly a 
generator. Also the __iter__ method should return the iterator.

 >>> values = [1, 2, 3]
 >>> mock_foo = MagicMock()
 >>> mock_foo.iter.return_value.__iter__.return_value = iter(values)
 >>> list(mock_foo.iter())
     [1, 2, 3]

I'm adding this as a recipe to the "examples" page as I got it wrong on 
the first attempt... :-)

Michael
> All the best,
>
> Michael Foord
>
>> I would like to mock the class and patch Foo.iter. I have tried a 
>> number of things without luck.
>>
>> class TestFoo(PatchedTestCase):
>>     _partitions = []
>>
>>     def partitions(self):
>>         for p in self._partitions:
>>             yield p
>>
>>     def postSetUpPreRun(self):
>>         self._partitions = [ 1, 2, 3, 4  ]
>>         rw = Mock(spec=Foo)
>>         self.mock_RollingWindow = rw
>>         rw.iter = Mock()
>>         rw.iter.side_effect = self.partitions
>>
>> This is following the pattern I've used for other methods, but 
>> doesn't work for an iterator... so, what is the proper approach please?
>>
>> Andrew
>>
>>
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>
>
> -- 
> http://www.voidspace.org.uk/
>
> May you do good and not evil
> May you find forgiveness for yourself and forgive others
> May you share freely, never taking more than you give.
> -- the sqlite blessinghttp://www.sqlite.org/different.html
>
>
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-- 
http://www.voidspace.org.uk/

May you do good and not evil
May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
-- the sqlite blessing http://www.sqlite.org/different.html

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