using pip3: module "importlib._bootstrap" has no attribute "SourceFileLoader" : <p>I have installed pip for python 3.6 on Ubuntu 14. After I run</p>

<pre><code>sudo apt-get install python3-pip
</code></pre>

<p>to install pip3, it works very well. However, after installation, when I am trying to run</p>

<pre><code>pip3 install packagename
</code></pre>

<p>to install a new package, something strange occurs:</p>

<pre><code>File "/usr/lib/python3/dist-packages/pkg_resources.py", line 1479, in &lt;module&gt;
 register_loader-type(importlib_bootstrap.SourceFileLoader, DefaultProvider)
AttributeError: module "importlib._bootstrap" has no attribute "SourceFileLoader"
</code></pre>

<p>It seems that I did nothing wrong, and I really cannot figure out the reason.</p>
