Honor 2-digit python version

cmake/OpenCVDetectPython.cmake

@@ -19,18 +19,25 @@ unset(HAVE_SPHINX CACHE)
 if(PYTHON_EXECUTABLE)
   if(PYTHON_VERSION_STRING)
     set(PYTHON_VERSION_MAJOR_MINOR "${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR}")
-    string(REGEX MATCH "[0-9]+.[0-9]+.[0-9]+" PYTHON_VERSION_FULL "${PYTHON_VERSION_STRING}")
+    set(PYTHON_VERSION_FULL "${PYTHON_VERSION_STRING}")
   else()
     execute_process(COMMAND ${PYTHON_EXECUTABLE} --version
       ERROR_VARIABLE PYTHON_VERSION_FULL
       ERROR_STRIP_TRAILING_WHITESPACE)
 
     string(REGEX MATCH "[0-9]+.[0-9]+" PYTHON_VERSION_MAJOR_MINOR "${PYTHON_VERSION_FULL}")
-    string(REGEX MATCH "[0-9]+.[0-9]+.[0-9]+" PYTHON_VERSION_FULL "${PYTHON_VERSION_FULL}")
+  endif()
+
+  if("${PYTHON_VERSION_FULL}" MATCHES "[0-9]+.[0-9]+.[0-9]+")
+    set(PYTHON_VERSION_FULL "${CMAKE_MATCH_0}")
+  elseif("${PYTHON_VERSION_FULL}" MATCHES "[0-9]+.[0-9]+")
+    set(PYTHON_VERSION_FULL "${CMAKE_MATCH_0}")
+  else()
+    unset(PYTHON_VERSION_FULL)
   endif()
 
   if(NOT ANDROID AND NOT IOS)
-    if(CMAKE_VERSION VERSION_GREATER 2.8.8)
+    if(CMAKE_VERSION VERSION_GREATER 2.8.8 AND PYTHON_VERSION_FULL)
       find_host_package(PythonLibs ${PYTHON_VERSION_FULL} EXACT)
     else()
       find_host_package(PythonLibs ${PYTHON_VERSION_FULL})