title: Modules in the same package cannot import each other
body: <p>I am currently using Python 3.7.</p>
  
  <p>My project has the following structure:</p>
  
  <pre><code>runner.py
      pkg1/
          __init__.py (empty)
          mod1.py
          mod1_helpers.py
  </code></pre>
  
  <p>In mod1.py:</p>
  
  <pre><code>import mod1_helpers
  
  # call some functions in mod1_helpers.py
  </code></pre>
  
  <p>In runner.py:</p>
  
  <pre><code>import pkg1.mod1
  </code></pre>
  
  <p>When I run runner.py, Python threw the following error:  </p>
  
  <pre><code>File "..\pkg1\mod1.py", line 1, in &lt;module&gt;  
      import mod1_helpers  
  ModuleNotFoundError: No module named 'mod1_helpers'
  </code></pre>
  
  <p>The issue resolves when I manually add the path to pkg1 to sys.path in runner.py.</p>
  
  <p>Could someone please advise the proper way to resolve this issue?</p>