code: def is_android(filename):
      
      if not filename:
          return None
  
      with open(filename, "rb") as fd:
          f_bytes = fd.read()
          return is_android_raw(f_bytes)
  
      return None
docs: Return the type of the file
  
          @param filename : the filename
          @rtype : "APK", "DEX", None