Python 参数解析 : metavar and action=store_true together

Question

我在 Python 中使用 argparse 模块来解析在命令行界面中键入的参数。我有以下对子解析器对象的 add_argument 调用:

submit_parser.add_argument('-pv','--provision',metavar='PROVISION', dest='PROVISION',
                                 help='provision system',
                                 action='store_true', default=False, required=False)

我收到这个错误:

Traceback (most recent call last):
  File "./scripts/tp4", line 94, in <module> 
    main()
  File "./scripts/tp4", line 74, in main 
    modloader.loadModules(sub_parsers)
  File "/usr/lib/python2.6/site-packages/tp4/cli/Moduleloader.py", line 66, in loadModules 
    registered_modules[module_name].setSubparserArgs(module_sub_parser)
  File "/usr/lib/python2.6/site-packages/tp4/cli/modules/AutotestModule.py", line 135, in setSubparserArgs
    action='store_true', default=False, required=False)
  File "/usr/share/tp4/cli/zip/argparse.zip/argparse.py", line 1302, in add_argument
    TypeError: __init__() got an unexpected keyword argument 'metavar'

如果我删除 action 或 metavar 参数，它会起作用。为什么两个人不能在一起？在 http://docs.python.org/dev/library/argparse.html 的 argparse 文档中没有关于此限制的内容。 .

在此先感谢您的帮助

Answer 1

metavar 只对位置参数有意义(想想命令行末尾的文件名)或者当一个参数接受它自己的参数时(比如 --input-files foo.txt bar.txt).

您的 --provision 参数是一个标志，因为您将 action 设置为 store_true。它不接受任何参数(即 nargs 未设置)。因此，拥有元变量没有意义。

来自 the argparse documentation :

When ArgumentParser generates help messages, it need some way to refer to each expected argument. By default, ArgumentParser objects use the dest value as the “name” of each object. By default, for positional argument actions, the dest value is used directly, and for optional argument actions, the dest value is uppercased. So, a single positional argument with dest='bar' will be referred to as bar. A single optional argument --foo that should be followed by a single command-line argument will be referred to as FOO.