title: Drake source install on Ubuntu 20.04: Could NOT find Python
body: <p>I'm trying to build drake from source on Ubuntu 20.04 by following instructions from <a href="https://drake.mit.edu/from_source.html" rel="nofollow noreferrer">here</a>. I already checked that my system meets all the requirements, and was ale to successfully run the mandatory platform-specific setup script (and it completed saying: 'install_prereqs: success'). However, when I try to run cmake to build the python bindings, I'm confronted with the following error:</p>
  <pre><code>CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):
    Could NOT find Python (missing: Python_NumPy_INCLUDE_DIRS NumPy) (found
    suitable exact version &quot;3.8.10&quot;)
  Call Stack (most recent call first):
    /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:393 (_FPHSA_FAILURE_MESSAGE)
    /usr/share/cmake-3.16/Modules/FindPython/Support.cmake:2214 (find_package_handle_standard_args)
    /usr/share/cmake-3.16/Modules/FindPython.cmake:304 (include)
    CMakeLists.txt:240 (find_package)
  
  
  -- Configuring incomplete, errors occurred!
  </code></pre>
  <p>I can't seem to think of any reason why this is happening (I made sure to remove conda from my PATH variable following the note <a href="https://drake.mit.edu/python_bindings.html#installation" rel="nofollow noreferrer">here</a>. Any help around this issue is much appreciated!</p>
  <p>EDIT: Want to mention that I'm trying to install Drake from <a href="https://github.com/RobotLocomotion/drake/pull/16147" rel="nofollow noreferrer">this PR</a> that includes a feature I need access to.</p>