python中的argparse模块(参数解析)_python parser.add_argument 可否不输入

import argparse
parse = argparse.ArgumentParser()
parse.add_argument("a", help="params means")
parse.add_argument("-C", "--gc", default="count")
parse.add_argument("--ga", help="params means ga",dest='simple_value',choices=['A', 'B', 'C', 0])
parse.add_argument("--gb", help="params means gb",action="store_const",const='value-to-store')
args = parse.parse_args()
print args.simple_value,args.gb,args.gc

### add_argument 说明
不带'--'的参数
    调用脚本时必须输入值
    参数输入的顺序与程序中定义的顺序一致
'-'的参数
    可不输入    add_argument("-a")
    类似有'--'的shortname，但程序中的变量名为定义的参数名
'--'参数
    参数别名: 只能是1个字符，区分大小写
        add_argument("-shortname","--name", help="params means")，但代码中不能使用shortname
    dest: 参数在程序中对应的变量名称 add_argument("a",dest='code_name')
    default: 参数默认值
    help: 参数作用解释  add_argument("a", help="params means")
    type : 默认string  add_argument("c", type=int)
    action:

    store：默认action模式，存储值到指定变量。
    store_const：存储值在参数的const部分指定，多用于实现非布尔的命令行flag。
    store_true / store_false：布尔开关。 store_true.默认为False，输入则为true。 store_flase 相反
    append：存储值到列表，该参数可以重复使用。
    append_const：存储值到列表，存储值在参数的const部分指定。
    count: 统计参数简写输入的个数  add_argument("-c", "--gc", action="count")
    version 输出版本信息然后退出。

    const:配合action="store_const|append_const"使用，默认值
    choices:输入值的范围 add_argument("--gb", choices=['A', 'B', 'C', 0])
    required : 默认False, 若为 True, 表示必须输入该参数


==================================================================================
    Keyword Arguments:
        - option_strings -- A list of command-line option strings which    should be associated with this action.
        - dest -- The name of the attribute to hold the created object(s)
        - nargs -- The number of command-line arguments that should be  consumed. By default, one argument will be consumed and a single   value will be produced.
                     Other values include:

                - N (an integer) consumes N arguments (and produces a list)
                - '?' consumes zero or one arguments
                - '*' consumes zero or more arguments (and produces a list)
                - '+' consumes one or more arguments (and produces a list)

                    Note that the difference between the default and nargs=1 is that with the default, a single value will be produced, while with  nargs=1, a list containing a single value will be produced.
        - const -- The value to be produced if the option is specified and the  option uses an action that takes no values.
        - default -- The value to be produced if the option is not specified.
        - type -- A callable that accepts a single string argument, and returns the converted value.  
                    The standard Python types str, int,  float, and complex are useful examples of such callables.  If None,  str is used.
        - choices -- A container of values that should be allowed.
                    If not None,  after a command-line argument has been converted to the appropriate type, an exception will be raised if it is not a member of this collection.
        - required -- True if the action must always be specified at the command line. This is only meaningful for optional command-line  arguments.
        - help -- The help string describing the argument.
        - metavar -- The name to be used for the option's argument with the  help string. If None, the 'dest' value will be used as the name.

• 创建子parse,每个子parse对应自己的输入参数

  

使用帮助

# python args_subparse.py -h
usage: args_subparse.py [-h] {create,list,delete} ...

positional arguments:
  {create,list,delete}  commands
    list                Listcontents
    create              Create a directory
    delete              Remove a directory

optional arguments:
  -h, --help            show this help message and exit
  
# python args_subparse.py create -h
usage: args_subparse.py create [-h] [--read-only] dirname

positional arguments:
  dirname      New directoryto create

optional arguments:
  -h, --help   show this help message and exit
  --read-only  Setpermissions to prevent writing to the directory
  
# python args_subparse.py delete -h
usage: args_subparse.py delete [-h] [--recursive] dirname

positional arguments:
  dirname          The directory to remove

optional arguments:
  -h, --help       show this help message and exit
  --recursive, -r  Remove thecontents of the directory, too
 
# python args_subparse.py list -h
usage: args_subparse.py list [-h] dirname

positional arguments:
  dirname     Directory tolist

optional arguments:
  -h, --help  show this help message and exit

多个subparser 使用同样定义的参数
# add_help=False,必须指定，否则报-h重复定义
parents_parser = argparse.ArgumentParser(add_help=False)
parents_parser.add_argument('--foo', dest="foo", action='store_true')
parents_parser.add_argument('--bar', dest="bar", action='store_false')
parents_parser.add_argument('--baz', dest="baz", action='store_false')

parser = argparse.ArgumentParser()
subparsers = parser.add_subparsers(help='commands')
m_parser = subparsers.add_parser("mysql", parents=[parents_parser], help="mysql method")
m_parser.set_defaults(func=sub_mysql)
o_parser = subparsers.add_parser("oracle", parents=[parents_parser], help="oracle method")
o_parser.set_defaults(func=sub_oracle)
args = parser.parse_args()


参考
http://blog.csdn.net/songuooo/article/details/8373086
http://www.2cto.com/kf/201208/149418.html
http://stackoverflow.com/questions/7498595/python-argparse-add-argument-to-multiple-subparsers