This is solved, I was being dumb. Please see second EDIT below
This isn’t really language specific, but if it helps I’m using Python. I can get the parameters just fine with the Traitlets module, but I’m still a novice really and figuring out which patterns to use is challenging.
Say you have a bunch of command line parameters. Some are booleans, where their presence means True, absence means False. Other parameters must accept one text string, and others can be used multiple times to build a list of strings.
It feels inefficient/wrong to use a bunch of IF/THEN/ELSE statements to decide what to do with the parameters, and prone to edge case errors. Is there a pattern that would invoke the correct method based on the combination of input parameters?
Examples:
app thing --dry-run --create --name=newname01 --name=newname02 --verbose
app thing --create --name=newname01 --name=newname02 --name=newname03
app job --cancel -i 01 -i 02 -i 03
EDIT: Via the Traitlets module, I get those arguments parsed and accessible as self.argname, so getting them into my app is working great. It’s just deciding what to do with them that is confusing me.
Thank you, sorry for my noobness.
EDIT2: I think I understand where I’m going wrong:
I’m creating subcommands based on objects, not actions. i.e. appname thing --action should really be appname action --thing. Once things are divided up into actions, assigning things to those actions will be much, much easier and straightforward.
Sorry for a confusing and fairly pointless post :(
As a few others mentioned, the argparse module from the stdlib is the way to go for Python. It takes care of most of this for you in an optimized way. Here’s a minimal example of the above:
#!/bin/env python3 import argparse # Setup main parser parser = argparse.ArgumentParser( prog="app", description="App that manages things and jobs", ) parser.add_argument( "-v", "--verbose", action="store_true", ) subparsers = parser.add_subparser( help="Sub commands", dest="command", ) # Setup sub-parsers thing_parser = subparsers.add_parser( "thing", help="Manage things", ) # thing_parser args thing_parser.add_argument( "--dry_run", action="store_true", help="dry run", ) thing_parser.add_argument( "--create", action="store_true", help="Create thing", ) thing_parser.add_argument( "--name", action="store", type=str, required=True, nargs="+", help="Thing name", ) job_parser = subparsers.add_parser( "job", help="Manage jobs", ) job_parser.add_argument( "--cancel", "-c", action="store_true", help="Cancel job", ) job_parser.add_argument( "--index", "-i", action="store", type=int, required=True, nargs="+", help="Job index", ) def main(): args=parser.parse_args() if args.verbose: print("Verbose mode") # Match-Case statement for cleaner logic match args.command: case "thing": # thing logic and function calls here case "job": # job logic and function calls here case _: parser.print_usage() if __name__ == "__main__": main()That’s an awesome answer, thank you very much. It’s much more elegant than my stuff!
You’re very welcome! I’ve spent a lot of time with Python and really think that argparse as of 3.x makes most non-stdlib libraries for parsing are unnecessary. You get a ton of functionally and ability to add end-user documentation as you go, while abstracting away some of the basics like type casting/checking
The addition of Match-Case, while not adding much, functionally, does a LOT for readability and keeping logic clear.
I’m so annoyed with myself for using
Traitletsfor command line argument parsing! Your solution usingargparsehas so many more useful options, like the ability to define a mutually exclusive group of arguments.Sigh. I live and learn and code a bunch more lol.
No reason to be annoyed with yourself. It’s part of the process of learning. In starting with
Traitlets, you tried something new to you and between that and refactoring to useargparse, you’ve given yourself more practice writing code and learned a bit more about available libraries. And, at the same time, you’ve worked through the logic of your CLI design, building a better understanding of ways to organize arguments.
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It’s never pointless. Command-line arguments are often tricky to get right, especially when your program can do a lot of different things.
Strings and human beings are two things that mix to create really tough problems.
I just wish I had thought things through correctly but I guess that’s part of becoming a more experienced coder. Arrrrggh! I’m so annoyed I wasted time on the otherwise excellent
Traitlets’ argument parsing!I said it a billion times before but: failing is how you learn. You discover why you’re wrong, and then you understand how to be right.
That’s why I think juniors should not use ChatGPT but that’s another story…
Python has a builtin argparse module. You should use that. It does all of the heavy lifting and logic for you.
I was doing it wrong. I was trying to do
appname thing --actionwhen I should have been doingappname action --thing. Thank you for commenting, I’m sorry to waste your time.
What module are you currently using? I think the built-in module argparse should solve your problem but maybe I’m misunderstanding what you’re asking for.
I was doing it wrong. I was trying to do
appname thing --actionwhen I should have been doingappname action --thing. Thank you for commenting, I’m sorry to waste your time.No worries, this ain’t Stackoverflow ;-)
I already have the arguments parsed, the bit that I’m confused about is where I decide what to do based on those various combinations of arguments.
I’m using Traitlets.
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Seems like a for statement and a case statement could work.
Detect numargs
For a = 0 to numargs
Get core command on arg a (probably read until you hit an equals sign or a space), trim and lcase
Select Case core command
Case “thing”
Do stuff
Case “–name” Get part after equals and do stuff
Case “-i” Get next arg and increment a
End select
I was doing it wrong. I was trying to do
appname thing --actionwhen I should have been doingappname action --thing. Thank you for commenting, I’m sorry to waste your time.No worries, it was fun trying to figure out a solution to the problem regardless.
