Python: Added basic structure

.github/ci/packages.apt

@@ -7,5 +7,8 @@ libignition-utils1-cli-dev
 libtinyxml2-dev
 liburdfdom-dev
 libxml2-utils
+python3-dev
+python3-distutils
 python3-psutil
+python3-pybind11
 ruby-dev

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.10.2 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.12 FATAL_ERROR)
 
 if(COMMAND CMAKE_POLICY)
   CMAKE_POLICY(SET CMP0003 NEW)
@@ -21,6 +21,16 @@ set (BUILD_SDF ON CACHE INTERNAL "Build SDF" FORCE)
 find_package(ignition-cmake2 2.10 REQUIRED)
 set(IGN_CMAKE_VER ${ignition-cmake2_VERSION_MAJOR})
 
+########################################
+# Python interfaces vars
+option(USE_SYSTEM_PATHS_FOR_PYTHON_INSTALLATION
+      "Install python modules in standard system paths in the system"
+      OFF)
+
+option(USE_DIST_PACKAGES_FOR_PYTHON
+      "Use dist-packages instead of site-package to install python modules"
+      OFF)
+
 if (BUILD_SDF)
   ign_configure_project(
     NO_IGNITION_PREFIX
@@ -70,7 +80,7 @@ if (BUILD_SDF)
       # A module's location is usually a directory, but for
       # binary modules
       # it's a .so file.
-      execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c" "import re, ${module}; print(re.compile('/__init__.py.*').sub('',${module}.__file__))"
+      execute_process(COMMAND "${Python3_EXECUTABLE}" "-c" "import re, ${module}; print(re.compile('/__init__.py.*').sub('',${module}.__file__))"
         RESULT_VARIABLE _${module}_status
         OUTPUT_VARIABLE _${module}_location
         ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
@@ -114,6 +124,26 @@ if (BUILD_SDF)
   ign_find_package(ignition-common5 COMPONENTS graphics REQUIRED_BY usd)
   set(IGN_COMMON_VER ${ignition-common5_VERSION_MAJOR})
 
+  ########################################
+  # Python interfaces
+  if (NOT PYTHON3_FOUND)
+    IGN_BUILD_WARNING("Python is missing: Python interfaces are disabled.")
+    message (STATUS "Searching for Python - not found.")
+  else()
+    message (STATUS "Searching for Python - found version ${Python3_VERSION}.")
+
+    set(PYBIND11_PYTHON_VERSION 3)
+    find_package(pybind11 2.4 QUIET)
+
+    if (${pybind11_FOUND})
+      find_package(Python3 ${IGN_PYTHON_VERSION} REQUIRED COMPONENTS Development)
+      message (STATUS "Searching for pybind11 - found version ${pybind11_VERSION}.")
+  	else()
+  		IGN_BUILD_WARNING("pybind11 is missing: Python interfaces are disabled.")
+  		message (STATUS "Searching for pybind11 - not found.")
+  	endif()
+  endif()
+
   ########################################
   # Find PXR
   ign_find_package(pxr QUIET REQUIRED_BY usd PKGCONFIG pxr)
@@ -126,6 +156,9 @@ if (BUILD_SDF)
   add_subdirectory(sdf)
   add_subdirectory(conf)
   add_subdirectory(doc)
+  if (${pybind11_FOUND})
+  	add_subdirectory(python)
+  endif()
 endif(BUILD_SDF)
 
 ########################################

examples/python/README.md

@@ -0,0 +1,19 @@
+# sdformat Python API
+
+This example shows how to use sdformat's Python API.
+
+In the
+[examples/python](https://github.com/ignitionrobotics/sdformat/blob/main/examples/python)
+folder there is a Python script that shows how to make use of this API.
+
+> If you compiled sdformat from source you should modify your `PYTHONPATH`:
+>
+>  ```bash
+>  export PYTHONPATH=$PYTHONPATH:<path to ws>/install/lib/python
+>    ```
+
+Now you can run the example:
+
+```bash
+$ python3 python_sdformat.py
+```

examples/python/python_sdformat.py

@@ -0,0 +1,15 @@
+# Copyright (C) 2022 Open Source Robotics Foundation
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#       http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sdformat

python/CMakeLists.txt

@@ -0,0 +1,63 @@
+if(WIN32 AND CMAKE_BUILD_TYPE STREQUAL "Debug")
+  # pybind11 logic for setting up a debug build when both a debug and release
+  # python interpreter are present in the system seems to be pretty much broken.
+  # This works around the issue.
+  set(PYTHON_LIBRARIES "${PYTHON_DEBUG_LIBRARIES}")
+endif()
+
+
+if(USE_SYSTEM_PATHS_FOR_PYTHON_INSTALLATION)
+  if(${CMAKE_VERSION} VERSION_LESS "3.12.0")
+    execute_process(
+      COMMAND "${PYTHON_EXECUTABLE}" -c "if True:
+  from distutils import sysconfig as sc
+  print(sc.get_python_lib(plat_specific=True))"
+      OUTPUT_VARIABLE Python3_SITEARCH
+      OUTPUT_STRIP_TRAILING_WHITESPACE)
+  else()
+    # Get install variable from Python3 module
+    # Python3_SITEARCH is available from 3.12 on, workaround if needed:
+    find_package(Python3 COMPONENTS Interpreter)
+  endif()
+
+  if(USE_DIST_PACKAGES_FOR_PYTHON)
+    string(REPLACE "site-packages" "dist-packages" IGN_PYTHON_INSTALL_PATH ${Python3_SITEARCH})
+  endif()
+else()
+  # If not a system installation, respect local paths
+  set(IGN_PYTHON_INSTALL_PATH ${IGN_LIB_INSTALL_DIR}/python)
+endif()
+
+# Set the build location and install location for a CPython extension
+function(configure_build_install_location _library_name)
+  # Install library for actual use
+  install(TARGETS ${_library_name}
+    DESTINATION "${IGN_PYTHON_INSTALL_PATH}"
+  )
+endfunction()
+
+pybind11_add_module(sdformat SHARED
+  src/sdf/_ignition_sdformat_pybind11.cc
+)
+
+target_link_libraries(sdformat PRIVATE
+  ${PROJECT_LIBRARY_TARGET_NAME}
+)
+
+configure_build_install_location(sdformat)
+
+if (BUILD_TESTING)
+  set(python_tests
+  )
+
+  foreach (test ${python_tests})
+    add_test(NAME ${test}.py COMMAND
+    "${Python3_EXECUTABLE}" "${CMAKE_SOURCE_DIR}/python/test/${test}.py")
+
+    set(_env_vars)
+    list(APPEND _env_vars "PYTHONPATH=${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/python/")
+    list(APPEND _env_vars "LD_LIBRARY_PATH=${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}:$ENV{LD_LIBRARY_PATH}")
+    set_tests_properties(${test}.py PROPERTIES
+      ENVIRONMENT "${_env_vars}")
+  endforeach()
+endif()

python/src/sdf/_ignition_sdformat_pybind11.cc

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <pybind11/pybind11.h>
+
+PYBIND11_MODULE(sdformat, m) {
+  m.doc() = "sdformat Python Library.";
+}