code: def page_exists_on_disk(self, slug):
          '''Return true if post directory and post file both exist.'''
  
          r = False
          page_dir = os.path.join(self.dirs['source'], slug)
          page_file_name = os.path.join(page_dir, slug + '.md')
          if os.path.isdir(page_dir):
              if os.path.isfile(page_file_name):
                  r = True
          return f page_exists_on_disk(self, slug):
          '''Return true if post directory and post file both exist.'''
  
          r = False
          page_dir = os.path.join(self.dirs['source'], slug)
          page_file_name = os.path.join(page_dir, slug + '.md')
          if os.path.isdir(page_dir):
              if os.path.isfile(page_file_name):
                  r = True
          return r
docs: Return true if post directory and post file both exist.