title: Error when installing mpi4py on Ubuntu instance
body: <p>I'm trying to install mpi4py on my Ubuntu 18.04 instance. I have python3.6.5 installed.</p>
  
  <p>First I try <code>sudo apt-get build-dep python-mpi4py</code> and I get: </p>
  
  <blockquote>
    <p>Reading package lists... Done E: You must put some 'source' URIs in
    your sources.list</p>
  </blockquote>
  
  <p>I then try to install simply with <code>pip install mpi4py</code>. I get a long error message and I include some of the most important parts below:</p>
  
  <pre><code>checking for library 'lmpe' ...
    /home/ubuntu/anaconda3/envs/tensorflow_p36/bin/mpicc -pthread -B /home/ubuntu/anaconda3/envs/tensorflow_p36/compiler_compat -Wl,--sysroot=/ -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -c _configtest.c -o _configtest.o
    --------------------------------------------------------------------------
    The Open MPI wrapper compiler was unable to find the specified compiler
    x86_64-conda_cos6-linux-gnu-cc in your PATH.
  
    Note that this compiler was either specified at configure time or in
    one of several possible environment variables.
    --------------------------------------------------------------------------
    failure.
  </code></pre>
  
  <p>This failure occurs for most libraries. I include just one of the many, and</p>
  
  <pre><code>  warning: build_clib: command '/home/ubuntu/anaconda3/envs/tensorflow_p36/bin/mpicc' failed with exit status 1
  
    warning: build_clib: building optional library "vt-mpi" failed
  
  
    checking for library 'vt-hyb' ...
    /home/ubuntu/anaconda3/envs/tensorflow_p36/bin/mpicc -pthread -B /home/ubuntu/anaconda3/envs/tensorflow_p36/compiler_compat -Wl,--sysroot=/ -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -c _configtest.c -o _configtest.o
    --------------------------------------------------------------------------
    The Open MPI wrapper compiler was unable to find the specified compiler
    x86_64-conda_cos6-linux-gnu-cc in your PATH.
  
    Note that this compiler was either specified at configure time or in
    one of several possible environment variables.
  </code></pre>
  
  <p>Running <code>which mpcc</code> gives:</p>
  
  <pre><code>(tensorflow_p36) ubuntu@ip-172-31-35-200:~$ which mpicc
  /home/ubuntu/anaconda3/envs/tensorflow_p36/bin/mpicc
  </code></pre>
  
  <p>How can I add the specified compiler x86_64-conda_cos6-linux-gnu-cc to my PATH in order to resolve this error?</p>