python 命令行参数 parser.add_arguement 中各参数的意思

class Action(_AttributeHolder):
“”"Information about how to convert command line strings to Python objects.

Action objects are used by an ArgumentParser to represent the information
needed to parse a single argument from one or more strings from the
command line. The keyword arguments to the Action constructor are also
all attributes of Action instances.
 
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.
"""