title: error message "ModuleNotFoundError: No module named 'context_locals'" occurred while import tool
body: <p>When I import module <code>tool</code>, I get the following error message,</p>
  
  <pre><code>  File "/Users/bird/Desktop/various-examples-of-web-crawlers/venv/lib/python3.7/site-packages/tool/__init__.py", line 11, in &lt;module&gt;
      from context_locals import app, local
  ModuleNotFoundError: No module named 'context_locals'
  </code></pre>
  
  <p>Operating system：macOS Sierra 10.12.6</p>
  
  <p>IDE: pycharm</p>
  
  <p>Code:</p>
  
  <pre><code>import urllib.request
  
  import urllib.parse
  
  import re
  
  import tool
  
  if __name__ == '__main__':
  
      #引入工具类
      self_tool = tool.Tool()
  </code></pre>
  
  <p>I tried to find a solution on google, but failed.</p>