选题[tech]: 20210816 Parse command-line arguments with argparse in Python

sources/tech/20210816 Parse command-line arguments with argparse in Python.md

sources/tech/20210816 Parse command-line arguments with argparse in Python.md

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+[#]: subject: "Parse command-line arguments with argparse in Python"
+[#]: via: "https://opensource.com/article/21/8/python-argparse"
+[#]: author: "Moshe Zadka https://opensource.com/users/moshez"
+[#]: collector: "lujun9972"
+[#]: translator: " "
+[#]: reviewer: " "
+[#]: publisher: " "
+[#]: url: " "
+
+Parse command-line arguments with argparse in Python
+======
+Use the argparse module to enable options in your Python applications.
+![Python options][1]
+
+There are several third-party libraries for command-line argument parsing, but the standard library module `argparse` is no slouch either.
+
+Without adding any more dependencies, you can write a nifty command-line tool with useful argument parsing.
+
+### Argument parsing in Python
+
+When parsing command-line arguments with `argparse`, the first step is to configure an `ArgumentParser` object. This is often done at the global module scope since merely _configuring_ the parser has no side effects.
+
+
+```
+import argparse
+
+PARSER = argparse.ArgumentParser()
+```
+
+The most important method on `ArgumentParser` is `.add_argument()`. It has a few variants. By default, it adds an argument that expects a value.
+
+
+```
+`PARSER.add_argument("--value")`
+```
+
+To see it in action, call the method `.parse_args()`:
+
+
+```
+`PARSER.parse_args(["--value", "some-value"])`[/code] [code]`Namespace(value='some-value')`
+```
+
+It's also possible to use the syntax with `=`:
+
+
+```
+`PARSER.parse_args(["--value=some-value"])`[/code] [code]`Namespace(value='some-value')`
+```
+
+You can also specify a short "alias" for a shorter command line when typed into the prompt:
+
+
+```
+`PARSER.add_argument("--thing", "-t")`
+```
+
+It's possible to pass either the short option:
+
+
+```
+`PARSER.parse_args("-t some-thing".split())`[/code] [code]`Namespace(value=None, thing='some-thing')`
+```
+
+or the long one:
+
+
+```
+`PARSER.parse_args("--thing some-thing".split())`[/code] [code]`Namespace(value=None, thing='some-thing')`
+```
+
+### Types
+
+There are more types of arguments available. The two most popular ones, after the default, are boolean and counting. The booleans come with a variant that defaults to true, and one that defaults to false.
+
+
+```
+PARSER.add_argument("--active", action="store_true")
+PARSER.add_argument("--no-dry-run", action="store_false", dest="dry_run")
+PARSER.add_argument("--verbose", "-v", action="count")
+```
+
+This means that `active` is `False` unless `--active` is passed, and `dry_run` is `True` unless `--no-dry-run` is passed. Short options without value can be juxtaposed.
+
+Passing all the arguments results in a non-default state:
+
+
+```
+`PARSER.parse_args("--active --no-dry-run -vvvv".split())`[/code] [code]`Namespace(value=None, thing=None, active=True, dry_run=False, verbose=4)`
+```
+
+The default is somewhat less exciting:
+
+
+```
+`PARSER.parse_args("".split())`[/code] [code]`Namespace(value=None, thing=None, active=False, dry_run=True, verbose=None)`
+```
+
+### Subcommands
+
+Though classic Unix commands "did one thing, and did it well," the modern tendency is to do "several closely related actions."
+
+The examples of `git`, `podman`, and `kubectl` can show how popular the paradigm is. The `argparse` library supports that too:
+
+
+```
+MULTI_PARSER = argparse.ArgumentParser()
+subparsers = MULTI_PARSER.add_subparsers()
+get = subparsers.add_parser("get")
+get.add_argument("--name")
+get.set_defaults(command="get")
+search = subparsers.add_parser("search")
+search.add_argument("--query")
+search.set_defaults(command="search")
+
+[/code] [code]`MULTI_PARSER.parse_args("get --name awesome-name".split())`[/code] [code]`Namespace(name='awesome-name', command='get')`[/code] [code]`MULTI_PARSER.parse_args("search --query name~awesome".split())`[/code] [code]`Namespace(query='name~awesome', command='search')`
+```
+
+### Anatomy of a program
+
+One way to use `argparse` is to structure the program as follows:
+
+
+```
+## my_package/__main__.py
+import argparse
+import sys
+
+from my_package import toplevel
+
+parsed_arguments = toplevel.PARSER.parse_args(sys.argv[1:])
+toplevel.main(parsed_arguments)
+
+[/code] [code]
+
+## my_package/toplevel.py
+
+PARSER = argparse.ArgumentParser()
+## .add_argument, etc.
+
+def main(parsed_args):
+
+    ...
+
+    # do stuff with parsed_args
+```
+
+In this case, running the command is done with `python -m my_package`. Alternatively, you can use the [`console_scripts`][2] entry points in the package's setup.
+
+### Summary
+
+The `argparse` module is a powerful command-line argument parser. There are many more features that have not been covered here. The limit is your imagination.
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/21/8/python-argparse
+
+作者：[Moshe Zadka][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://opensource.com/users/moshez
+[b]: https://github.com/lujun9972
+[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/bitmap_0.png?itok=PBXU-cn0 (Python options)
+[2]: https://python-packaging.readthedocs.io/en/latest/command-line-scripts.html#the-console-scripts-entry-point