code: def from_filename(self, filename):
          '''
          Convert an absolute filename into key.
          '''
          i = len(self.base_directory)
          if filename[:i] != self.base_directory:
              raise ValueError('Filename needs to start with "%s";\nyou passed "%s".' % (self.base_directory, filename))
  
          if filename.endswith(self.extension):
              if len(self.extension) > 0:
                  j = -len(self.extension)
              else:
                  j = None
              return self.key_transformer.from_path(tuple(filename[i:j].strip('/').split('/'))f from_filename(self, filename):
          '''
          Convert an absolute filename into key.
          '''
          i = len(self.base_directory)
          if filename[:i] != self.base_directory:
              raise ValueError('Filename needs to start with "%s";\nyou passed "%s".' % (self.base_directory, filename))
  
          if filename.endswith(self.extension):
              if len(self.extension) > 0:
                  j = -len(self.extension)
              else:
                  j = None
              return self.key_transformer.from_path(tuple(filename[i:j].strip('/').split('/')))
docs: Convert an absolute filename into key.