Make using Python easier

- Move Pipfile to the root of the project, so docs and CMake builds
  can access it

- Fix python/CMakeLists.txt

- Document

CMakeLists.txt

@@ -55,6 +55,7 @@ install(FILES ${ENHANCEDENUM_CONFIG}
 
 install(DIRECTORY ${ENHANCEDENUM_INCLUDE_DIR}/ DESTINATION include)
 
+set(ENHANCEDENUM_BUILD_TESTS OFF CACHE BOOL "Build tests")
 if(ENHANCEDENUM_BUILD_TESTS)
   enable_testing()
 endif()
@@ -64,7 +65,6 @@ if(ENHANCEDENUM_BUILD_DOCS)
   add_subdirectory(docs)
 endif()
 
-set(ENHANCEDENUM_BUILD_TESTS OFF CACHE BOOL "Build tests")
 if(ENHANCEDENUM_BUILD_TESTS)
   add_subdirectory(cxx/tests)
 endif()

docs/installation.rst

@@ -27,9 +27,7 @@ The Enhanced Enum library specific CMake variables are:
      $ python setup.py build
      $ python setup.py install
 
-  ...but does some extra bootstrapping to build out-of-source. The
-  package is thus installed in the current site-packages. You can also
-  do normal in-source build for greater control.
+  ...but does some extra bootstrapping to build out-of-source.
 
 - ``ENHANCEDENUM_BUILD_TESTS``: Build tests for the C++ and/or Python
   packages
@@ -44,12 +42,35 @@ imported target ``EnhancedEnum::EnhancedEnum``:
    find_package(EnhancedEnum)
    target_link_libraries(my-target EnhancedEnum::EnhancedEnum)
 
-Docs, EnumECG and unit tests *all* require Python when being built. A
-build environment can be bootstrapped using the ``Pipfile`` under
-the ``python/`` directory:
+Python environment
+------------------
+
+Docs, EnumECG and unit tests *all* require Python when being built. To
+use the CMake targets, a suggested approach is to create a build
+directory under the sources where the project ``Pipfile `` is
+available.
+
+.. code-block:: console
+
+   $ mkdir /path/to/repository/build
+   $ cd /path/to/repository/build
+   $ pipenv install --dev
+   $ pipenv run cmake                           \
+   >   -D ENHANCEDENUM_BUILD_DOCS:BOOL=ON       \
+   >   -D ENHANCEDENUM_BUILD_TESTS:BOOL=ON      \
+   >   ..
+   $ make && make test
+
+However, ``make install`` target may not make much sense with this
+workflow, as it will only install :mod:`enumecg` to the current
+virtualenv. If want to install development version of the EnumECG
+library via CMake, you should use an external virtualenv:
 
 .. code-block:: console
 
-  $ cd /path/to/repository/python
-  $ pipenv install --dev
-  $ pipenv shell
+   (venv) $ cd /path/to/build/dir
+   (venv) $ cmake -D ENHANCEDENUM_BUILD_PYTHON:BOOL=ON /path/to/repository
+   (venv) $ make && make install
+
+It is of course possible to build and install EnumECG by invoking a
+more typical in-source build.

python/CMakeLists.txt

@@ -3,7 +3,9 @@ include(FindPython)
 find_package(Python)
 
 if(Python_FOUND)
+  get_target_property(PYTHON_EXECUTABLE Python::Interpreter LOCATION)
   set(PYTHON_BUILD_DIR "${CMAKE_CURRENT_BINARY_DIR}/build/lib")
+  file(MAKE_DIRECTORY ${PYTHON_BUILD_DIR})
 
   set(ENUMECG_SETUP "${CMAKE_CURRENT_SOURCE_DIR}/setup.py")
   set(ENUMECG_OUTPUT "${PYTHON_BUILD_DIR}/timestamp")