title: pulp.solvers.PulpSolverError: PuLP: cannot execute cplex
body: <p>I am trying to solve an MIP using PuLP on a Mac. I have already added the directory
  <code>'/Applications/CPLEX_Studio1210/cplex/python/3.7/x86-64_osx',</code>
  to my <code>PYTHONPATH</code>. But whenever I try </p>
  
  <p><code>prob.solve(CPLEX_CMD())</code>,</p>
  
  <p>I receive the following error message:</p>
  
  <pre><code>File "/Users/xxxx/opt/anaconda3/envs/pulposm/lib/python3.7/site-packages/pulp/solvers.py", line 468, in actualSolve
      raise PulpSolverError("PuLP: cannot execute "+self.path)
  pulp.solvers.PulpSolverError: PuLP: cannot execute cplex.
  </code></pre>