How to use the pcpp.pcmd.FileAction function in pcpp

def __init__(self, argv):
        if len(argv) < 2:
            argv = [argv[0], '--help']
        argp = argparse.ArgumentParser(prog='pcpp',
            description=
    '''A pure universal Python C (pre-)preprocessor implementation very useful for
    pre-preprocessing header only C++ libraries into single file includes and
    other such build or packaging stage malarky.''',
            epilog=
    '''Note that so pcpp can stand in for other preprocessor tooling, it
    ignores any arguments it does not understand.''')
        argp.add_argument('inputs', metavar = 'input', default = [sys.stdin], nargs = '*', action = FileAction, help = 'Files to preprocess (use \'-\' for stdin)')
        argp.add_argument('-o', dest = 'output', metavar = 'path', type = argparse.FileType('wt'), default=sys.stdout, nargs = '?', help = 'Output to a file instead of stdout')
        argp.add_argument('-D', dest = 'defines', metavar = 'macro[=val]', nargs = 1, action = 'append', help = 'Predefine name as a macro [with value]')
        argp.add_argument('-U', dest = 'undefines', metavar = 'macro', nargs = 1, action = 'append', help = 'Pre-undefine name as a macro')
        argp.add_argument('-N', dest = 'nevers', metavar = 'macro', nargs = 1, action = 'append', help = 'Never define name as a macro, even if defined during the preprocessing.')
        argp.add_argument('-I', dest = 'includes', metavar = 'path', nargs = 1, action = 'append', help = "Path to search for unfound #include's")
        #argp.add_argument('--passthru', dest = 'passthru', action = 'store_true', help = 'Pass through everything unexecuted except for #include and include guards (which need to be the first thing in an include file')
        argp.add_argument('--passthru-defines', dest = 'passthru_defines', action = 'store_true', help = 'Pass through but still execute #defines and #undefs if not always removed by preprocessor logic')
        argp.add_argument('--passthru-unfound-includes', dest = 'passthru_unfound_includes', action = 'store_true', help = 'Pass through #includes not found without execution')
        argp.add_argument('--passthru-unknown-exprs', dest = 'passthru_undefined_exprs', action = 'store_true', help = 'Unknown macros in expressions cause preprocessor logic to be passed through instead of executed by treating unknown macros as 0L')
        argp.add_argument('--passthru-comments', dest = 'passthru_comments', action = 'store_true', help = 'Pass through comments unmodified')
        argp.add_argument('--passthru-magic-macros', dest = 'passthru_magic_macros', action = 'store_true', help = 'Pass through double underscore magic macros unmodified')
        argp.add_argument('--disable-auto-pragma-once', dest = 'auto_pragma_once_disabled', action = 'store_true', default = False, help = 'Disable the heuristics which auto apply #pragma once to #include files wholly wrapped in an obvious include guard macro')
        argp.add_argument('--line-directive', dest = 'line_directive', metavar = 'form', default = '#line', nargs = '?', help = "Form of line directive to use, defaults to #line, specify nothing to disable output of line directives")
        argp.add_argument('--debug', dest = 'debug', action = 'store_true', help = 'Generate a pcpp_debug.log file logging execution')
        argp.add_argument('--time', dest = 'time', action = 'store_true', help = 'Print the time it took to #include each file')
        argp.add_argument('--filetimes', dest = 'filetimes', metavar = 'path', type = argparse.FileType('wt'), default=None, nargs = '?', help = 'Write CSV file with time spent inside each included file, inclusive and exclusive')

def __init__(self, option_strings, dest, **kwargs):
        super(FileAction, self).__init__(option_strings, dest, **kwargs)