How to mock generators with mock.patch
<p>I have gone through the page <a href="https://docs.python.org/3/library/unittest.mock-examples.html" rel="noreferrer">https://docs.python.org/3/library/unittest.mock-examples.html</a> and i see that they have listed an example on how to mock generators</p>

<p>I have a code where i call a generator to give me a set of values that i save as a dictionary. I want to mock the calls to this generator in my unit test.</p>

<p>I have written the following code and it does not work. </p>

<p>Where am i going wrong?</p>

<pre><code>In [7]: items = [(1,'a'),(2,'a'),(3,'a')]

In [18]: def f():
    print "here"
    for i in [1,2,3]:
        yield i,'a'

In [8]: def call_f():
   ...:     my_dict = dict(f())
   ...:     print my_dict[1]
   ...: 

In [9]: call_f()
"here"
a

In [10]: import mock


In [18]: def test_call_f():
    with mock.patch('__main__.f') as mock_f:
        mock_f.iter.return_value = items
        call_f()
   ....: 

In [19]: test_call_f()
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
&lt;ipython-input-19-33ca65a4f3eb&gt; in &lt;module&gt;()
----&gt; 1 test_call_f()

&lt;ipython-input-18-92ff5f1363c8&gt; in test_call_f()
      2     with mock.patch('__main__.f') as mock_f:
      3         mock_f.iter.return_value = items
----&gt; 4         call_f()

&lt;ipython-input-8-a5cff08ebf69&gt; in call_f()
      1 def call_f():
      2     my_dict = dict(f())
----&gt; 3     print my_dict[1]

KeyError: 1
</code></pre>