Groovy Beta: Python error in Arch Linux install

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I am following the install instructions for groovy beta and in section 2, when I do:

cmake .. -DCMAKE_INSTALL_PREFIX=/opt/ros/groovy -DPYTHON_EXECUTABLE=/usr/bin/python2 -DPYTHON_INCLUDE_DIR=/usr/include/python2.7 -DPYTHON_LIBRARY=/usr/lib/libpython2.7.so -DSETUPTOOLS_DEB_LAYOUT=OFF

I get the following error:

-- The C compiler identification is GNU 4.7.2
-- The CXX compiler identification is GNU 4.7.2
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Using CATKIN_DEVEL_PREFIX: /home/kevin/groovy_underlay/build/devel
-- Found PythonInterp: /usr/bin/python2 (found version "2.7.3") 
-- Could NOT find PY_em (missing:  PY_EM) 
CMake Error at catkin/cmake/empy.cmake:28 (message):
  Unable to find either executable 'empy' or Python module 'em'...  try
  installing package 'python-empy'
Call Stack (most recent call first):
  catkin/cmake/all.cmake:136 (include)
  CMakeLists.txt:15 (include)


-- Configuring incomplete, errors occurred!

How do I get arch to find the python-empy I installed earlier in step 1?