Submodules

pybind11 supports the idea of specifying C++ bindings in submodules of other pybind11 modules as described in the pybind11 docs. PYB11Generator works on a module by module basis (assuming you have a base *.py file describing what should be in the module), so supporting submodules requires telling PYB11Generator whether to treat such a module file as a submodule, and independently whether this module will in turn have any submodules. Both of these tasks are handled by passing arguments to the invocation of the PYB11generateModule function. PYB11Generator’s CMake rule PYB11Generator_add_module (documented in Using CMake to build PYB11Generator modules) provides simplifed support for creating and using submodules via the optional keywords IS_SUBMODULE and SUBMODULES.

As an example, suppose we want have two submodules Asub and Bsub of module my_module:

my_module
|
|-- Asub
|-- Bsub

We can write three Python PYB11Generator module files for binding each of these modules as normal.

my_module_PYB11.py:

from PYB11Generator import *

"""A dummy main module that has a couple of submodules"""

Asub_PYB11.py:

from PYB11Generator import *

PYB11includes = ['"A.hh"']

class A:

    def pyinit(self):
        "Default constructor"

    def func(self, x="int"):
        "A::func"
        return "int"

Bsub_PYB11.py:

from PYB11Generator import *

PYB11includes = ['"B.hh"']

class B:

    def pyinit(self):
        "Default constructor"

    def func(self, x="int"):
        "B::func"
        return "int"

Now we can create the module my_module with its submodules Asub and Bsub by creating three CMake targets:

PYB11Generator_add_module(my_module
  SUBMODULES Asub Bsub
  DEPENDS Asub Bsub)

PYB11Generator_add_module(Asub
  IS_SUBMODULE ON)

PYB11Generator_add_module(Bsub
  IS_SUBMODULE ON)

Note that our only new requirements are that we need to specify to the rule building my_module that it has two submodules, while for both Asub and Bsub we need to flip on the IS_SUBMODULE flag to treat them as submodules. At compilation time this results in Asub and Bsub being built as static libraries which are linked to the final dynamic module my_module.