python-3.x 如何使用argparse创建像git这样的命令组？

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我正在尝试弄清楚如何正确使用内置的argparse模块来获得与git等工具类似的输出，在git中，我可以显示一个很好的帮助，所有的“根命令”都被很好地分组，即：

$ git --help
usage: git [--version] [--help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           [--super-prefix=<path>] [--config-env=<name>=<envvar>]
           <command> [<args>]

These are common Git commands used in various situations:

start a working area (see also: git help tutorial)
   clone     Clone a repository into a new directory
   init      Create an empty Git repository or reinitialize an existing one

work on the current change (see also: git help everyday)
   add       Add file contents to the index
   mv        Move or rename a file, a directory, or a symlink
   restore   Restore working tree files
   rm        Remove files from the working tree and from the index

examine the history and state (see also: git help revisions)
   bisect    Use binary search to find the commit that introduced a bug
   diff      Show changes between commits, commit and working tree, etc
   grep      Print lines matching a pattern
   log       Show commit logs
   show      Show various types of objects
   status    Show the working tree status

grow, mark and tweak your common history
   branch    List, create, or delete branches
   commit    Record changes to the repository
   merge     Join two or more development histories together
   rebase    Reapply commits on top of another base tip
   reset     Reset current HEAD to the specified state
   switch    Switch branches
   tag       Create, list, delete or verify a tag object signed with GPG

collaborate (see also: git help workflows)
   fetch     Download objects and refs from another repository
   pull      Fetch from and integrate with another repository or a local branch
   push      Update remote refs along with associated objects

'git help -a' and 'git help -g' list available subcommands and some
concept guides. See 'git help <command>' or 'git help <concept>'
to read about a specific subcommand or concept.
See 'git help git' for an overview of the system.

下面是我的尝试：

from argparse import ArgumentParser

class FooCommand:
    def __init__(self, subparser):
        self.name = "Foo"
        self.help = "Foo help"
        subparser.add_parser(self.name, help=self.help)

class BarCommand:
    def __init__(self, subparser):
        self.name = "Bar"
        self.help = "Bar help"
        subparser.add_parser(self.name, help=self.help)

class BazCommand:
    def __init__(self, subparser):
        self.name = "Baz"
        self.help = "Baz help"
        subparser.add_parser(self.name, help=self.help)

def test1():
    parser = ArgumentParser(description="Test1 ArgumentParser")
    root = parser.add_subparsers(dest="command", description="All Commands:")

    # Group1
    FooCommand(root)
    BarCommand(root)

    # Group2
    BazCommand(root)

    args = parser.parse_args()
    print(args)

def test2():
    parser = ArgumentParser(description="Test2 ArgumentParser")

    # Group1
    cat1 = parser.add_subparsers(dest="command", description="Category1 Commands:")
    FooCommand(cat1)
    BarCommand(cat1)

    # Group2
    cat2 = parser.add_subparsers(dest="command", description="Category2 Commands:")
    BazCommand(cat2)

    args = parser.parse_args()
    print(args)

如果运行test1，将得到：

$ python mcve.py --help
usage: mcve.py [-h] {Foo,Bar,Baz} ...

Test1 ArgumentParser

options:
  -h, --help     show this help message and exit

subcommands:
  All Commands:

  {Foo,Bar,Baz}
    Foo          Foo help
    Bar          Bar help
    Baz          Baz help

显然这不是我想要的，在那里我只看到了一个平面列表中的所有命令，没有分组或任何东西...所以下一个合乎逻辑的尝试是尝试将它们分组。但如果我运行test2，我会得到：

$ python mcve.py --help
usage: mcve.py [-h] {Foo,Bar} ...
mcve.py: error: cannot have multiple subparser arguments

这显然意味着我没有正确地使用argparse来完成手头的任务。那么，是否有可能使用argparse来实现与git类似的行为呢？在过去，我一直依赖于“hacks”，所以我认为这里的最佳实践是使用add_subparsers的概念，但似乎我没有正确理解这个概念。

argparse本身并不支持这个功能--你不能嵌套子解析器，所以如果你想使用argparse来构建这样的cli，你需要在argparse之上构建大量的逻辑，你可以设置nargs=argparse.REMAINDER来收集子命令和参数，而不用argparse来解析它们，这意味着我们可以构建这样的东西：

import argparse
import copy

class Command:
    def __init__(self):
        self.subcommands = {}
        self.parser = argparse.ArgumentParser()

    def add_subcommand(self, name, sub):
        self.subcommands[name] = sub

    def add_argument(self, *args, **kwargs):
        return self.parser.add_argument(*args, **kwargs)

    def parse_args(self, args=None):
        if not self.subcommands:
            args = self.parser.parse_args(args)
            return args

        p = copy.deepcopy(self.parser)
        p.add_argument("subcommand")
        p.add_argument("args", nargs=argparse.REMAINDER)
        args = p.parse_args(args)

        try:
            sub = self.subcommands[args.subcommand]
        except KeyError:
            return self.parser.parse_args(args)

        sub_args = sub.parse_args(args.args)

        for attr in dir(sub_args):
            if attr.startswith("_"):
                continue
            setattr(args, attr, getattr(sub_args, attr))

        return args

def main():
    root = Command()
    root.add_argument("-v", "--verbose", action="count")

    cmd1 = Command()
    cmd1_foo = Command()
    cmd1_foo.add_argument("-n", "--name")
    cmd1.add_subcommand("foo", cmd1_foo)
    root.add_subcommand("cmd1", cmd1)

    cmd2 = Command()
    cmd2_bar = Command()
    cmd2_bar.add_argument("-s", "--size", type=int)
    cmd2.add_subcommand("bar", cmd2_bar)
    root.add_subcommand("cmd2", cmd2)

    print(root.parse_args())

if __name__ == "__main__":
    main()

这是可怕的，丑陋的，结构不良的，但它意味着我们可以做到这一点：

$ python argtest.py --verbose cmd1 foo --name lars
Namespace(verbose=1, subcommand='foo', args=['--name', 'lars'], name='lars')

或者这个：

$ python argtest.py --verbose cmd2 bar --size 10
Namespace(verbose=1, subcommand='bar', args=['--size', '10'], size=10)

如果你不想局限于argparse，像Click和Typer这样的库会让事情变得更简单，例如，上面的命令可以像这样使用Click来实现：

import click

@click.group()
def main():
    pass

@main.group()
def cmd1():
    pass

@cmd1.command()
@click.option('-n', '--name')
def foo(name):
    pass

@main.group()
def cmd2():
    pass

@cmd2.command()
@click.option('-s', '--size', type=int)
def bar():
    pass

if __name__ == '__main__':
    main()

好多了！

python-3.x 如何使用argparse创建像git这样的命令组？

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