Python 3 - ImportError: No module named
<p><strong>Situation:</strong><br>
Given this project structure:</p>

<pre><code>project/
  app/
    __init__.py (empty)
    stamp.py
  tests/
    test.py
  main.py
</code></pre>

<p>In <code>main.py</code> and <code>test.py</code> I am trying to import the functionality of <code>stamp.py</code> via:</p>

<pre><code>from app.stamp import Timestamp 
</code></pre>

<p><code>Timestamp</code> gets imported in <code>main.py</code> but not in <code>test.py</code> where I get this error: </p>

<pre><code>ImportError: No module named 'app'
</code></pre>

<p><strong>Question</strong>:<br>
How can I in python 3.5 import functionality of <code>stamp.py</code> in <code>test.py</code>?</p>