[TIP] mock os.walk

Staple, Danny (BSKYB) DStaple at nds.com
Thu Mar 22 08:16:03 PDT 2012

You are only creating the iter once, so it is the correct behavior.  You could create a tiny function to build you the mock with a fresh iter each time, and call it in the patch statement.

-----Original Message-----
From: testing-in-python-bounces at lists.idyll.org [mailto:testing-in-python-bounces at lists.idyll.org] On Behalf Of Andrea Crotti
Sent: 22 March 2012 15:05
To: Testing in Python
Subject: Re: [TIP] mock os.walk

On 03/22/2012 02:47 PM, Andrea Crotti wrote:
> Looking around I found out that this:
> my_mock = Mock(return_value=iter(test_dir))
> actually works perfectly, even if I'm not sure why...
> I would still like to know why my MagicMock is not returning anything
> though..

Puff I finally solved all my problems and all the tests are passing :)

I found another thing which I think is at least counter-intuitive.

This below will not work as expected:

my_mock = Mock(return_value=iter(test_dir))

@patch('os.walk', new=my_mock)
def myfun2():
     for r, ds, df in os.walk('.'):
         print(r, ds, df)

@patch('os.walk', new=my_mock)
def myfun3():
     for r, ds, df in os.walk('.'):
         print(r, ds, df)


because the iterator is consumed the first run and in the second run there it will just return the empty list.
Is it the desired behaviour?

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