argparse.Action¶

class argparse.Action(option_strings, dest, nargs=None, const=None, default=None, type=None, choices=None, required=False, help=None, metavar=None)[source]¶

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.