'This checker factory expects to get the location of a file.
The file should conform to the format required by
L{FilePasswordDB} (using defaults for all
initialization parameters).'

def generateChecker(self, argstring):

    from twisted.python.filepath import FilePath
    if (not argstring.strip()):
        raise ValueError(('%r    requires    a    filename' % self.authType))
    elif (not FilePath(argstring).isfile()):
        self.errorOutput.write(('%s:    %s\n' % (invalidFileWarning, argstring)))
    return FilePasswordDB(argstring)
