argparse 中action参数

argparse内置6种动作可以在解析到一个参数时进行触发：

store 保存参数值，可能会先将参数值转换成另一个数据类型。若没有显式指定动作，则默认为该动作。

store_const 保存一个被定义为参数规格一部分的值，而不是一个来自参数解析而来的值。这通常用于实现非布尔值的命令行标记。

store_ture/store_false 保存相应的布尔值。这两个动作被用于实现布尔开关。

append 将值保存到一个列表中。若参数重复出现，则保存多个值。

append_const 将一个定义在参数规格中的值保存到一个列表中。

version 打印关于程序的版本信息，然后退出

import argparseparser = argparse.ArgumentParser()parser.add_argument('-s', action='store', dest='simple_value',        help='Store a simple value')parser.add_argument('-c', action='store_const', dest='constant_value',        const='value-to-store',        help='Store a constant value')parser.add_argument('-t', action='store_true', default=False,        dest='boolean_switch',        help='Set a switch to true')parser.add_argument('-f', action='store_false', default=False,        dest='boolean_switch',        help='Set a switch to false')parser.add_argument('-a', action='append', dest='collection',        default=[],        help='Add repeated values to a list')parser.add_argument('-A', action='append_const', dest='const_collection',        const='value-1-to-append',        default=[],        help='Add different values to list')parser.add_argument('-B', action='append_const', dest='const_collection',        const='value-2-to-append',        help='Add different values to list')parser.add_argument('--version', action='version', version='%(prog)s 1.0')results = parser.parse_args()print 'simple_value     =', results.simple_valueprint 'constant_value   =', results.constant_valueprint 'boolean_switch   =', results.boolean_switchprint 'collection       =', results.collectionprint 'const_collection =', results.const_collection

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$ python argparse_action.py -husage: argparse_action.py [-h] [-s SIMPLE_VALUE] [-c] [-t] [-f]                          [-a COLLECTION] [-A] [-B] [--version]optional arguments:  -h, --help       show this help message and exit  -s SIMPLE_VALUE  Store a simple value  -c               Store a constant value  -t               Set a switch to true  -f               Set a switch to false  -a COLLECTION    Add repeated values to a list  -A               Add different values to list  -B               Add different values to list  --version        show program's version number and exit$ python argparse_action.py -s valuesimple_value     = valueconstant_value   = Noneboolean_switch   = Falsecollection       = []const_collection = []$ python argparse_action.py -csimple_value     = Noneconstant_value   = value-to-storeboolean_switch   = Falsecollection       = []const_collection = []$ python argparse_action.py -tsimple_value     = Noneconstant_value   = Noneboolean_switch   = Truecollection       = []const_collection = []$ python argparse_action.py -fsimple_value     = Noneconstant_value   = Noneboolean_switch   = Falsecollection       = []const_collection = []$ python argparse_action.py -a one -a two -a threesimple_value     = Noneconstant_value   = Noneboolean_switch   = Falsecollection       = ['one', 'two', 'three']const_collection = []$ python argparse_action.py -B -Asimple_value     = Noneconstant_value   = Noneboolean_switch   = Falsecollection       = []const_collection = ['value-2-to-append', 'value-1-to-append']$ python argparse_action.py --versionargparse_action.py 1.0