Unexpected behavior of no_args_is_help with 0 or 1 commands

[jacob-bush-shopify]

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the Typer documentation, with the integrated search.
• I already searched in Google "How to X in Typer" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to Typer but to Click.

Example Code

Example 1

I expect help when invoked with no args

import typer

cli = typer.Typer(no_args_is_help=True)

if __name__ == "__main__":
    cli()

Actually raises an exception

$ python cli.py
AssertionError: Could not get a command for this Typer instance

Example 2

I expect help when invoked with no args

import typer

cli = typer.Typer(no_args_is_help=True)

@cli.command("1") 
def _1():
    print(1)

if __name__ == "__main__":
    cli()

Actually prints "1"

$ python cli.py
1

Example 3

I expect help when invoked with no args

import typer

cli = typer.Typer(no_args_is_help=True)

@cli.command("1") 
def _1():
    print(1)

@cli.command("2") 
def _2():
    print(2)

if __name__ == "__main__":
    cli()

Works as expected (though this breaks code relying on the behaviour of the 1-command typer app)

$ python cli.py
Usage: cli.py [OPTIONS] COMMAND [ARGS]...

Options:
  --install-completion [bash|zsh|fish|powershell|pwsh]
                                  Install completion for the specified shell.
  --show-completion [bash|zsh|fish|powershell|pwsh]
                                  Show completion for the specified shell, to
                                  copy it or customize the installation.
  --help                          Show this message and exit.

Commands:
  1
  2

Description

When no_args_is_help=True is set on my Typer application, I expect that the application will print the help text when it is called with no arguments.

When 2+ commands are registered, no_args_is_help works as expected.

However, there are two cases where this does not hold:

• When there are 0 commands registered on the application, an exception is raised
• When there is 1 command registered on the application, the command is called in lieu of printing the help text.

Operating System

macOS

Typer Version

0.6.1

Python Version

3.9.12

[marcstreeter]

I solved this for myself with this gist.

[tiangolo]

Thanks for the report!

Let's think about each case individually.

2 commands

So, the case with 2 commands is working as expected, right?

1 command

For the case of one command, it's currently working as intended, at least that's how it was designed from the beginning. When there's an app with a single command, that command is called directly, there's no subcommand created for it. It's documented here: https://typer.tiangolo.com/tutorial/commands/#explicit-application

If you want it to be a subcommand you would need to do one of:

• Add another command (which you wouldn't want in this case)
• Add a callback, it can be just a no-op, but it would tell Typer that this app should be considered a "group" with subcommands, even if just one.

import typer

cli = typer.Typer(no_args_is_help=True)

@cli.command("1") 
def _1():
    print(1)

@cli.callback()
def callback():
    pass

if __name__ == "__main__":
    cli()

Then:

$ python demo.py  
                                                                            
 Usage: demo.py [OPTIONS] COMMAND [ARGS]...                                 
                                                                            
╭─ Options ────────────────────────────────────────────────────────────────╮
│ --install-completion          Install completion for the current shell.  │
│ --show-completion             Show completion for the current shell, to  │
│                               copy it or customize the installation.     │
│ --help                        Show this message and exit.                │
╰──────────────────────────────────────────────────────────────────────────╯
╭─ Commands ───────────────────────────────────────────────────────────────╮
│ 1                                                                        │
╰──────────────────────────────────────────────────────────────────────────╯

no command

I would actually consider an app with no command or callback to be an error, telling me that there's no command to run, not a help message telling me that the only thing I can do is get that help message. 🤔