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I am reading through argparse module. I got stuck as what to metavar and action means
>>> parser.add_argument('integers', metavar='N', type=int, nargs='+', ... help='an integer for the accumulator') >>> parser.add_argument('--sum', dest='accumulate', action='store_const', ... const=sum, default=max, ... help='sum the integers (default: find the max)') I might have missed but from what I read, I could not find definitions for metavar and action (action="store_const", etc). what do they actually mean?
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dest is equal to the first argument supplied to the add_argument() function, as illustrated. The second argument, radius_circle , is optional. A long option string --radius supplied to the add_argument() function is used as dest , as illustrated.
The store_true option automatically creates a default value of False. Likewise, store_false will default to True when the command-line argument is not present.
Positional Arguments add_argument('indir', type=str, help='Input dir for videos') created a positional argument. For positional arguments to a Python function, the order matters. The first value passed from the command line becomes the first positional argument.
Optional arguments are useful if you want to give the user a choice to enable certain features. To add an optional argument, simply omit the required parameter in add_argument() . args = parser. parse_args()if args.
Metavar: It provides a different name for optional argument in help messages. Provide a value for the metavar keyword argument within add_argument().
>>> parser = argparse.ArgumentParser() >>> parser.add_argument('--foo', metavar='YYY') >>> parser.add_argument('bar', metavar='XXX') >>> parser.parse_args('X --foo Y'.split()) Namespace(bar='X', foo='Y') >>> parser.print_help() usage: [-h] [--foo YYY] XXX positional arguments: XXX optional arguments: -h, --help show this help message and exit --foo YYY Reference: http://www.usatlas.bnl.gov/~caballer/files/argparse/add_argument.html
Action: Arguments can trigger different actions, specified by the action argument to add_argument(). There are six built-in actions that can be triggered when an argument is encountered:
store: Save the value, after optionally converting it to a different type. This is the default action taken if none is specified explicitly.
store_true/store_false: Save the appropriate boolean value.
store_const: Save a value defined as part of the argument specification, rather than a value that comes from the arguments being parsed. This is typically used to implement command line flags that aren’t booleans.
append: Save the value to a list. Multiple values are saved if the argument is repeated.
append_const: Save a value defined in the argument specification to a list.
version: Prints version details about the program and then exits.
Reference: http://bioportal.weizmann.ac.il/course/python/PyMOTW/PyMOTW/docs/argparse/index.html
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metavar is used in help messages in a place of an expected argument. See FOO is a default metavar here:
>>> parser = argparse.ArgumentParser() >>> parser.add_argument('--foo') >>> parser.add_argument('bar') >>> parser.parse_args('X --foo Y'.split()) Namespace(bar='X', foo='Y') >>> parser.print_help() usage: [-h] [--foo FOO] bar ... action defines how to handle command-line arguments: store it as a constant, append into a list, store a boolean value etc. There are several built-in actions available, plus it's easy to write a custom one.
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