def ExistingFileOrNone(fname):
if os.path.isfile(fname):<EOL><INDENT>return fname<EOL><DEDENT>elif fname.lower() == '<STR_LIT:none>':<EOL><INDENT>return None<EOL><DEDENT>else:<EOL><INDENT>raise ValueError("<STR_LIT>" % fname)<EOL><DEDENT>
Like `Existingfile`, but if `fname` is string "None" then return `None`.