元变量和动作在 Python 的 argparse 中意味着什么？

我正在通读 Argparse模块。我卡住了什么元变量和行动的意思

>>> 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)')

我可能错过了，但从我读到的，我无法找到定义的 metavar和 它们到底是什么意思？

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最佳答案

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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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:

  1. store: Save the value, after optionally converting it to a different type. This is the default action taken if none is specified explicitly.

  2. store_true/store_false: Save the appropriate boolean value.

  3. 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.

  4. append: Save the value to a list. Multiple values are saved if the argument is repeated.

  5. append_const: Save a value defined in the argument specification to a list.

  6. 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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