running cmake commands in python script

Question

Is it possible to run cmake commands in a python script? I want to set the boost libraries which I installed and compiled manually through the python code.I want something like set(BOOST_INCLUDEDIR "/path/to/boost/include") to happen via python script. So, before running cmake I want the cmake variables to set through the python code.

Answer 1

There are two ways of pre-initialising CMake variables before CMake processing starts, both using command-line arguments of cmake .

The simple one is to pass one or more variables to CMake using the -D command-line option. Something like this:

cmake -DBOOST_INCLUDEDIR:PATH="/path/to/boost/include" ...

The other option is to create an "initial cache file" (basically a file containing just set(...) CMake commands) and pass that initial cache file to CMake using -C :

echo 'set(BOOST_INCLUDEDIR "/path/to/boost/include" CACHE PATH "")' > initial_cache.cmake
cmake -C initial_cache.cmake ...

This option is intended for use the first time CMake is run with a given binary directory, ie before it creates its own CMakeCache.txt file.

How you can utilise one or both of these from your Python script depends on your particular setup.

Answer 2

Yes

Option 1 (if you invoke cmake via python)

By setting cmake cache variables from the command line. The syntax for defining this from the command line is as follows from here

-D <var>:<type>=<value>

So in your case, in the cmake list file

set(BOOST_INCLUDEDIR MY_BOOST_INCLUDE)

Then simply override that option when invoking cmake

cmake -DMY_BOOST_INCLUDE:STRING="/path/to/wherever"

Option 2 (if you want to invoke cmake at another point)

You can make a cmake module in python that sets the defines you want. For example, make a python script that populates my_module.cmake with any cache variables you want, ie

set(MY_BOOST_INCLUDE "script/generated/path")
#... other stuff you want to define

Then in your static cmake list file

include(my_module)

Answer 3

Some of CMake's find modules do support reading path hints from environment variables:

• "Users may set these hints or results as cache entries. [...] One may specify these as environment variables if they are not specified as CMake variables or cache entries."

• I prefer this method of setting find module directories, because it's something I could also set on system level and I don't have to give every single of my CMake projects the paths to my custom build libraries anymore.

• FindBoost.cmake is an good example, because it offers various environment variable:

   Boost_DIR BOOSTROOT BOOST_ROOT BOOST_INCLUDEDIR BOOST_LIBRARYDIR 

• Note : Those are considered "hints", since they will not overwrite any CMake cache values once boost was found.