title: ns3, Python3 has no module named 'ns'
body: <p>I am using a virtual box to build network simulator 3(ns3), Ubuntu version: Linux Server 20.04 LTS</p>
  
  <p>the Linux command that I had executed are</p>
  
  <pre><code>sudo apt-get update
  sudo apt-get upgrade
  sudo apt-get install gcc g++ python python3 -y
  sudo apt-get install python3-setuptools git mercurial -y
  sudo apt-get install zip unzip  
  apt-get install cmake libc6-dev libc6-dev-i386 libclang-6.0-dev llvm-6.0-dev automake -y
  
  sudo apt-get install -y python-gi-cairo 
  sudo apt-get install -y gir1.2-gtk-3.0  
  sudo apt-get install -y python-dev  
  sudo apt-get install -y python3-dev 
  sudo apt-get install -y qt5-default 
  sudo apt-get install -y python3-pygraphviz
  sudo apt install python3-pip
  sudo apt-get install -y graphviz libgraphviz-dev
  sudo pip3 install pygraphviz --install-option='--include-path=/usr/include/graphviz' --install-option='--library-path=/usr/lib/graphviz'
  </code></pre>
  
  <p>Then I use the bake to install the ns3 through following this page: <a href="https://www.nsnam.org/wiki/Installation#Installation_with_Bake" rel="nofollow noreferrer">install ns3 with bake</a></p>
  
  <p>although the "bake.py show" tell me that pygraphvix is Missing, but since it is not an essential dependency, so I ignore it and continue build the ns3</p>
  
  <p>after i successfully built the ns3, I follow the instruction <a href="https://www.nsnam.org/docs/manual/html/python.html#running-python-scripts" rel="nofollow noreferrer">here</a> to execute the "./waf shell" command in the folder "/source/ns-3.29"</p>
  
  <p>then I run the command and get the error:</p>
  
  <pre><code>root@ns3simulator:/home/ns3/source/ns-3.29# python3 examples/wireless/mixed-wired-wireless.py
  Traceback (most recent call last):
    File "examples/wireless/mixed-wired-wireless.py", line 54, in &lt;module&gt;
      import ns.applications
  ModuleNotFoundError: No module named 'ns'
  </code></pre>
  
  <p>Could anyone please help me for this?Thanks in advance.</p>