Include a more robust FindPythonLibs module for CMake

CMakeLists.txt

@@ -25,18 +25,9 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
 endif()
 string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE)
 
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/tools")
 set(Python_ADDITIONAL_VERSIONS 3.4 3.5 3.6 3.7)
-if (NOT ${PYBIND11_PYTHON_VERSION} STREQUAL "")
-  find_package(PythonLibs ${PYBIND11_PYTHON_VERSION} EXACT)
-  if (NOT PYTHONLIBS_FOUND)
-    find_package(PythonLibs ${PYBIND11_PYTHON_VERSION} REQUIRED)
-  endif()
-else()
-  find_package(PythonLibs REQUIRED)
-endif()
-# The above sometimes returns version numbers like "3.4.3+"; the "+" must be removed for the next line to work
-string(REPLACE "+" "" PYTHONLIBS_VERSION_STRING "+${PYTHONLIBS_VERSION_STRING}")
-find_package(PythonInterp ${PYTHONLIBS_VERSION_STRING} EXACT REQUIRED)
+find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} REQUIRED)
 
 if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Intel")
   CHECK_CXX_COMPILER_FLAG("-std=c++14" HAS_CPP14_FLAG)
@@ -86,14 +77,13 @@ endif()
 
 
 # Check if Eigen is available
-set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/tools")
 find_package(Eigen3 QUIET)
 
 # Include path for pybind11 header files
 include_directories(include)
 
 # Include path for Python header files
-include_directories(${PYTHON_INCLUDE_DIR})
+include_directories(${PYTHON_INCLUDE_DIRS})
 
 set(PYBIND11_HEADERS
   include/pybind11/attr.h
@@ -184,7 +174,7 @@ if (WIN32)
   set_target_properties(example PROPERTIES SUFFIX ".pyd")
 
   # Link against the Python shared library
-  target_link_libraries(example ${PYTHON_LIBRARY})
+  target_link_libraries(example ${PYTHON_LIBRARIES})
 elseif (UNIX)
   # It's quite common to have multiple copies of the same Python version
   # installed on one's system. E.g.: one copy from the OS and another copy

tools/FindPythonLibsNew.cmake

+# - Find python libraries
+# This module finds the libraries corresponding to the Python interpeter
+# FindPythonInterp provides.
+# This code sets the following variables:
+#
+#  PYTHONLIBS_FOUND           - have the Python libs been found
+#  PYTHON_PREFIX              - path to the Python installation
+#  PYTHON_LIBRARIES           - path to the python library
+#  PYTHON_INCLUDE_DIRS        - path to where Python.h is found
+#  PYTHON_SITE_PACKAGES       - path to installation site-packages
+#  PYTHON_IS_DEBUG            - whether the Python interpreter is a debug build
+#
+#  PYTHON_INCLUDE_PATH        - path to where Python.h is found (deprecated)
+#
+# A function PYTHON_ADD_MODULE(<name> src1 src2 ... srcN) is defined
+# to build modules for python.
+#
+# Thanks to talljimbo for the patch adding the 'LDVERSION' config
+# variable usage.
+
+#=============================================================================
+# Copyright 2001-2009 Kitware, Inc.
+# Copyright 2012 Continuum Analytics, Inc.
+#
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the names of Kitware, Inc., the Insight Software Consortium,
+# nor the names of their contributors may be used to endorse or promote
+# products derived from this software without specific prior written
+# permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#=============================================================================
+
+
+# Use the Python interpreter to find the libs.
+if(PythonLibsNew_FIND_REQUIRED)
+    find_package(PythonInterp ${PythonLibsNew_FIND_VERSION} REQUIRED)
+else()
+    find_package(PythonInterp ${PythonLibsNew_FIND_VERSION})
+endif()
+
+if(NOT PYTHONINTERP_FOUND)
+    set(PYTHONLIBS_FOUND FALSE)
+    return()
+endif()
+
+# According to http://stackoverflow.com/questions/646518/python-how-to-detect-debug-interpreter
+# testing whether sys has the gettotalrefcount function is a reliable, cross-platform
+# way to detect a CPython debug interpreter.
+#
+# The library suffix is from the config var LDVERSION sometimes, otherwise
+# VERSION. VERSION will typically be like "2.7" on unix, and "27" on windows.
+execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c"
+    "from distutils import sysconfig as s;import sys;import struct;
+print('.'.join(str(v) for v in sys.version_info));
+print(sys.prefix);
+print(s.get_python_inc(plat_specific=True));
+print(s.get_python_lib(plat_specific=True));
+print(s.get_config_var('SO'));
+print(hasattr(sys, 'gettotalrefcount')+0);
+print(struct.calcsize('@P'));
+print(s.get_config_var('LDVERSION') or s.get_config_var('VERSION'));
+"
+    RESULT_VARIABLE _PYTHON_SUCCESS
+    OUTPUT_VARIABLE _PYTHON_VALUES
+    ERROR_VARIABLE _PYTHON_ERROR_VALUE
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+if(NOT _PYTHON_SUCCESS MATCHES 0)
+    if(PythonLibsNew_FIND_REQUIRED)
+        message(FATAL_ERROR
+            "Python config failure:\n${_PYTHON_ERROR_VALUE}")
+    endif()
+    set(PYTHONLIBS_FOUND FALSE)
+    return()
+endif()
+
+# Convert the process output into a list
+string(REGEX REPLACE ";" "\\\\;" _PYTHON_VALUES ${_PYTHON_VALUES})
+string(REGEX REPLACE "\n" ";" _PYTHON_VALUES ${_PYTHON_VALUES})
+list(GET _PYTHON_VALUES 0 _PYTHON_VERSION_LIST)
+list(GET _PYTHON_VALUES 1 PYTHON_PREFIX)
+list(GET _PYTHON_VALUES 2 PYTHON_INCLUDE_DIR)
+list(GET _PYTHON_VALUES 3 PYTHON_SITE_PACKAGES)
+list(GET _PYTHON_VALUES 4 PYTHON_MODULE_EXTENSION)
+list(GET _PYTHON_VALUES 5 PYTHON_IS_DEBUG)
+list(GET _PYTHON_VALUES 6 PYTHON_SIZEOF_VOID_P)
+list(GET _PYTHON_VALUES 7 PYTHON_LIBRARY_SUFFIX)
+
+# Make sure the Python has the same pointer-size as the chosen compiler
+# Skip if CMAKE_SIZEOF_VOID_P is not defined
+if(CMAKE_SIZEOF_VOID_P AND (NOT "${PYTHON_SIZEOF_VOID_P}" STREQUAL "${CMAKE_SIZEOF_VOID_P}"))
+    if(PythonLibsNew_FIND_REQUIRED)
+        math(EXPR _PYTHON_BITS "${PYTHON_SIZEOF_VOID_P} * 8")
+        math(EXPR _CMAKE_BITS "${CMAKE_SIZEOF_VOID_P} * 8")
+        message(FATAL_ERROR
+            "Python config failure: Python is ${_PYTHON_BITS}-bit, "
+            "chosen compiler is  ${_CMAKE_BITS}-bit")
+    endif()
+    set(PYTHONLIBS_FOUND FALSE)
+    return()
+endif()
+
+# The built-in FindPython didn't always give the version numbers
+string(REGEX REPLACE "\\." ";" _PYTHON_VERSION_LIST ${_PYTHON_VERSION_LIST})
+list(GET _PYTHON_VERSION_LIST 0 PYTHON_VERSION_MAJOR)
+list(GET _PYTHON_VERSION_LIST 1 PYTHON_VERSION_MINOR)
+list(GET _PYTHON_VERSION_LIST 2 PYTHON_VERSION_PATCH)
+
+# Make sure all directory separators are '/'
+string(REGEX REPLACE "\\\\" "/" PYTHON_PREFIX ${PYTHON_PREFIX})
+string(REGEX REPLACE "\\\\" "/" PYTHON_INCLUDE_DIR ${PYTHON_INCLUDE_DIR})
+string(REGEX REPLACE "\\\\" "/" PYTHON_SITE_PACKAGES ${PYTHON_SITE_PACKAGES})
+
+# TODO: All the nuances of CPython debug builds have not been dealt with/tested.
+if(PYTHON_IS_DEBUG)
+    set(PYTHON_MODULE_EXTENSION "_d${PYTHON_MODULE_EXTENSION}")
+endif()
+
+if(CMAKE_HOST_WIN32)
+    set(PYTHON_LIBRARY
+        "${PYTHON_PREFIX}/libs/Python${PYTHON_LIBRARY_SUFFIX}.lib")
+elseif(APPLE)
+    set(PYTHON_LIBRARY
+        "${PYTHON_PREFIX}/lib/libpython${PYTHON_LIBRARY_SUFFIX}.dylib")
+else()
+    if(${PYTHON_SIZEOF_VOID_P} MATCHES 8)
+        set(_PYTHON_LIBS_SEARCH "${PYTHON_PREFIX}/lib64" "${PYTHON_PREFIX}/lib")
+    else()
+        set(_PYTHON_LIBS_SEARCH "${PYTHON_PREFIX}/lib")
+    endif()
+    #message(STATUS "Searching for Python libs in ${_PYTHON_LIBS_SEARCH}")
+    # Probably this needs to be more involved. It would be nice if the config
+    # information the python interpreter itself gave us were more complete.
+    find_library(PYTHON_LIBRARY
+        NAMES "python${PYTHON_LIBRARY_SUFFIX}"
+        PATHS ${_PYTHON_LIBS_SEARCH}
+        NO_DEFAULT_PATH)
+
+    # If all else fails, just set the name/version and let the linker figure out the path.
+    if(NOT PYTHON_LIBRARY)
+        set(PYTHON_LIBRARY python${PYTHON_LIBRARY_SUFFIX})
+    endif()
+endif()
+
+# For backward compatibility, set PYTHON_INCLUDE_PATH, but make it internal.
+SET(PYTHON_INCLUDE_PATH "${PYTHON_INCLUDE_DIR}" CACHE INTERNAL
+          "Path to where Python.h is found (deprecated)")
+
+MARK_AS_ADVANCED(
+  PYTHON_LIBRARY
+  PYTHON_INCLUDE_DIR
+)
+
+# We use PYTHON_INCLUDE_DIR, PYTHON_LIBRARY and PYTHON_DEBUG_LIBRARY for the
+# cache entries because they are meant to specify the location of a single
+# library. We now set the variables listed by the documentation for this
+# module.
+SET(PYTHON_INCLUDE_DIRS "${PYTHON_INCLUDE_DIR}")
+SET(PYTHON_LIBRARIES "${PYTHON_LIBRARY}")
+SET(PYTHON_DEBUG_LIBRARIES "${PYTHON_DEBUG_LIBRARY}")
+
+find_package_message(PYTHON
+    "Found PythonLibs: ${PYTHON_LIBRARY}"
+    "${PYTHON_EXECUTABLE}${PYTHON_VERSION}")