CMake: Don't depend on Python interpreter

This allows building against the Python libraries even when the
Python interpreter/executable is missing. The correct extensions
for the binary modules will be guessed, the tests will fail,
and the bytecode for any pure-Python modules will not be
precompiled.

cmake/macros/Python.cmake

@@ -39,7 +39,9 @@ function(add_python_target target)
       PREFIX ""
       SUFFIX "${PYTHON_EXTENSION_SUFFIX}")
 
-    install(TARGETS ${target} DESTINATION "${PYTHON_ARCH_INSTALL_DIR}/${slash_namespace}")
+    if(PYTHON_ARCH_INSTALL_DIR)
+      install(TARGETS ${target} DESTINATION "${PYTHON_ARCH_INSTALL_DIR}/${slash_namespace}")
+    endif()
   else()
     set_target_properties(${target} PROPERTIES
       OUTPUT_NAME "${basename}"

dtool/Package.cmake

@@ -7,10 +7,9 @@ set(WANT_PYTHON_VERSION ""
 
 find_package(PythonInterp ${WANT_PYTHON_VERSION} QUIET)
 find_package(PythonLibs ${PYTHON_VERSION_STRING} QUIET)
-if(PYTHONINTERP_FOUND AND PYTHONLIBS_FOUND)
+
+if(PYTHONLIBS_FOUND)
   set(PYTHON_FOUND ON)
-else()
-  set(PYTHON_FOUND OFF)
 endif()
 
 package_option(PYTHON DEFAULT ON
@@ -19,16 +18,26 @@ is also enabled, Python bindings will be generated.")
 
 # Also detect the optimal install paths:
 if(HAVE_PYTHON)
-  execute_process(
-    COMMAND ${PYTHON_EXECUTABLE}
-      -c "from distutils.sysconfig import get_python_lib; print(get_python_lib(False))"
-    OUTPUT_VARIABLE _LIB_DIR
-    OUTPUT_STRIP_TRAILING_WHITESPACE)
-  execute_process(
-    COMMAND ${PYTHON_EXECUTABLE}
-      -c "from distutils.sysconfig import get_python_lib; print(get_python_lib(True))"
-    OUTPUT_VARIABLE _ARCH_DIR
-    OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(WIN32 AND NOT CYGWIN)
+    set(_LIB_DIR ".")
+    set(_ARCH_DIR ".")
+  elseif(PYTHON_EXECUTABLE)
+    execute_process(
+      COMMAND ${PYTHON_EXECUTABLE}
+        -c "from distutils.sysconfig import get_python_lib; print(get_python_lib(False))"
+      OUTPUT_VARIABLE _LIB_DIR
+      OUTPUT_STRIP_TRAILING_WHITESPACE)
+    execute_process(
+      COMMAND ${PYTHON_EXECUTABLE}
+        -c "from distutils.sysconfig import get_python_lib; print(get_python_lib(True))"
+      OUTPUT_VARIABLE _ARCH_DIR
+      OUTPUT_STRIP_TRAILING_WHITESPACE)
+  else()
+    set(_LIB_DIR "")
+    set(_ARCH_DIR "")
+  endif()
+
+
   execute_process(
     COMMAND ${PYTHON_EXECUTABLE}
       -c "from sysconfig import get_config_var as g; print((g('EXT_SUFFIX') or g('SO'))[:])"