about things
fix argparse example to match actual pdsx code
- use tuple membership dispatch, not match/case
- add RawDescriptionHelpFormatter
- add async main pattern with sys.exit(asyncio.run())
- link to actual source
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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languages/python/patterns.md
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languages/python/patterns.md
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## argparse for CLIs
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argparse is stdlib and sufficient for most CLIs. subparsers give you git-style commands:
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argparse is stdlib. subparsers with aliases give you unix-style commands:
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```python
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import argparse
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parser = argparse.ArgumentParser(
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description="my tool",
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formatter_class=argparse.RawDescriptionHelpFormatter,
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)
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parser.add_argument("-r", "--repo", help="target repo")
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def main() -> int:
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parser = argparse.ArgumentParser(description="my tool")
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subparsers = parser.add_subparsers(dest="command")
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subparsers = parser.add_subparsers(dest="command")
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list_parser = subparsers.add_parser("list", aliases=["ls"])
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list_parser.add_argument("collection")
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list_parser.add_argument("--limit", type=int, default=50)
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list_parser = subparsers.add_parser("list", aliases=["ls"])
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list_parser.add_argument("collection")
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list_parser.add_argument("--limit", type=int, default=50)
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```
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dispatch with tuple membership to handle aliases:
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```python
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args = parser.parse_args()
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if not args.command:
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parser.print_help()
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return 1
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args = parser.parse_args()
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if args.command in ("list", "ls"):
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return await cmd_list(args.collection, args.limit)
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```
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match args.command:
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case "list" | "ls":
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return do_list(args.collection, args.limit)
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case _:
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parser.print_help()
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return 1
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async entry point pattern:
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```python
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async def async_main() -> int:
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# argparse and dispatch here
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return 0
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def main() -> NoReturn:
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sys.exit(asyncio.run(async_main()))
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```
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the pattern: parse once at the top, dispatch based on command, return exit codes.
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source: [pdsx/src/pdsx/cli.py](https://github.com/zzstoatzz/pdsx/blob/main/src/pdsx/cli.py)
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## module-level singletons
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