code: def findExtNum(self, extname=None, extver=1):
          
          extnum = None
          extname = extname.upper()
  
          if not self._isSimpleFits:
              for ext in self._image:
                  if (hasattr(ext,'_extension') and 'IMAGE' in ext._extension and
                      (ext.extname == extname) and (ext.extver == extver)):
                      extnum = ext.extnum
          else:
              log.info("Image is simple fits")
  
          return extnum
docs: Find the extension number of the give extname and extver.