code: def ensure_parent_dir(filename):
    
  
    # Ensure 'filename' corresponds to 'PATH_SCHEMA'.
    # Raise 'securesystemslib.exceptions.FormatError' on a mismatch.
    securesystemslib.formats.PATH_SCHEMA.check_match(filename)
  
    # Split 'filename' into head and tail, check if head exists.
    directory = os.path.split(filename)[0]
  
    if directory and not os.path.exists(directory):
      # mode = 'rwx------'. 448 (decimal) is 700 in octal.
      os.makedirs(directory, 448)
docs: <Purpose>
      To ensure existence of the parent directory of 'filename'.  If the parent
      directory of 'name' does not exist, create it.
  
      Example: If 'filename' is '/a/b/c/d.txt', and only the directory '/a/b/'
      exists, then directory '/a/b/c/d/' will be created.
  
    <Arguments>
      filename:
        A path string.
  
    <Exceptions>
      securesystemslib.exceptions.FormatError: If 'filename' is improperly
      formatted.
  
    <Side Effects>
      A directory is created whenever the parent directory of 'filename' does not
      exist.
  
    <Return>
      None.