Update CMakeLists.txt to support Python2 easily

Author: Gonzalo-Mier

CMakeLists.txt

@@ -4,7 +4,7 @@ project(matplotlib_cpp LANGUAGES CXX)
 include(GNUInstallDirs)
 set(PACKAGE_NAME matplotlib_cpp)
 set(INSTALL_CONFIGDIR ${CMAKE_INSTALL_LIBDIR}/${PACKAGE_NAME}/cmake)
-
+set(USING_PYTHON3 True)
 
 # Library target
 add_library(matplotlib_cpp INTERFACE)
@@ -17,19 +17,37 @@ target_compile_features(matplotlib_cpp INTERFACE
   cxx_std_11
 )
 # TODO: Use `Development.Embed` component when requiring cmake >= 3.18
-find_package(Python3 COMPONENTS Interpreter Development REQUIRED)
-target_link_libraries(matplotlib_cpp INTERFACE
-  Python3::Python
-  Python3::Module
-)
-find_package(Python3 COMPONENTS NumPy)
-if(Python3_NumPy_FOUND)
+if(USING_PYTHON3)
+  find_package(Python3 COMPONENTS Interpreter Development REQUIRED)
   target_link_libraries(matplotlib_cpp INTERFACE
-    Python3::NumPy
+    Python3::Python
+    Python3::Module
   )
+  find_package(Python3 COMPONENTS NumPy)
+  if(Python3_NumPy_FOUND)
+    target_link_libraries(matplotlib_cpp INTERFACE
+      Python3::NumPy
+    )
+  else()
+    target_compile_definitions(matplotlib_cpp INTERFACE WITHOUT_NUMPY)
+  endif()
 else()
-  target_compile_definitions(matplotlib_cpp INTERFACE WITHOUT_NUMPY)
+  find_package(Python2 COMPONENTS Interpreter Development REQUIRED)
+  target_link_libraries(matplotlib_cpp INTERFACE
+    Python2::Python
+    Python2::Module
+  )
+  find_package(Python2 COMPONENTS NumPy)
+  if(Python2_NumPy_FOUND)
+    target_link_libraries(matplotlib_cpp INTERFACE
+      Python2::NumPy
+    )
+  else()
+    target_compile_definitions(matplotlib_cpp INTERFACE WITHOUT_NUMPY)
+  endif()
 endif()
+
+
 install(
   TARGETS matplotlib_cpp
   EXPORT install_targets