Using CMake with setup.py - cmake

Question

For a project I build a C library and implict Python bindings (via GObject introspection) with CMake. I also want to distribute some Python helper modules using distutils. I am able to build and install the module with this CMakeLists.txt
find_program(PYTHON "python")
if (PYTHON)
set(SETUP_PY_IN "${CMAKE_CURRENT_SOURCE_DIR}/setup.py.in")
set(SETUP_PY "${CMAKE_CURRENT_BINARY_DIR}/setup.py")
set(DEPS "${CMAKE_CURRENT_SOURCE_DIR}/module/__init__.py")
set(OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/build")
configure_file(${SETUP_PY_IN} ${SETUP_PY})
add_custom_command(OUTPUT ${OUTPUT}
COMMAND ${PYTHON}
ARGS setup.py build
DEPENDS ${DEPS})
add_custom_target(target ALL DEPENDS ${OUTPUT})
install(CODE "execute_process(COMMAND ${PYTHON} ${SETUP_PY} install)")
endif()
and the following setup.py.in:
from distutils.core import setup, Extension
if __name__ == '__main__':
setup(name='foo',
version='${PACKAGE_VERSION}',
package_dir={ '': '${CMAKE_CURRENT_SOURCE_DIR}' },
packages=['module'])
Unfortunately, the build step is executed each time I run make. I guess, the problem is related to the output of the custom command which is a directory rather than a file. Now, is there any way to tell CMake to run python setup.py build only when setup.py.in or one of the sources changed?

Answer 1

Only files, not directories, can be reliably used as OUTPUT and DEPENDS. You could modify your custom command to also produce a timestamp file, something like this:
add_custom_command(
OUTPUT ${OUTPUT}/timestamp
COMMAND ${PYTHON} setup.py build
COMMAND ${CMAKE_COMMAND} -E touch ${OUTPUT}/timestamp
DEPENDS ${DEPS}
)
add_custom_target(target ALL DEPENDS ${OUTPUT}/timestamp)