title: pip is error,TypeError: __call__() takes exactly 2 arguments (1 given)
body: <h3>system</h3>
  
  <ul>
  <li>centos 7.2</li>
  <li>Python 2.7.5</li>
  </ul>
  
  <h3>install</h3>
  
  <p>I install <a href="https://github.com/NetEaseGame/git-webhook" rel="noreferrer">webhook</a></p>
  
  <pre><code>pip install webhook
  ### but hava error,then
  yum install python-devel -y
  ## go on,pip doesn't workding
  pip
  </code></pre>
  
  <h3>error</h3>
  
  <p>Enter the command contain pip.Then</p>
  
  <pre><code>[root@location src]# pip
  Traceback (most recent call last):
  File "/usr/bin/pip", line 5, in &lt;module&gt;
  from pkg_resources import load_entry_point
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 72, in &lt;module&gt;
  import packaging.requirements
  File "/usr/lib/python2.7/site-packages/packaging/requirements.py", line 59, in &lt;module&gt;
  MARKER_EXPR = originalTextFor(MARKER_EXPR())("marker")
  TypeError: __call__() takes exactly 2 arguments (1 given)
  </code></pre>
  
  <p>So,what should I do?!</p>