#28398: Allow management command invocation to suggest for incomplete commands?

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Vláďa Macek

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Jul 15, 2017, 12:37:50 PM7/15/17
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Hi everyone,

I had an idea that would save me time working with Django:

The manage.py wouldn't only print "Unknown command" when incomplete subcommand name given, but also print those available by substring search.

https://code.djangoproject.com/ticket/28398

I added a screenshot and a patch there.

In my opinion, such first implementation could be as simple as that. Smarter versions may come later.

As suggested by Tim Graham (thanks, Tim), I resort here for opinions.

Thank you,

Vlada Macek

Brice PARENT

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Jul 17, 2017, 3:49:12 AM7/17/17
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Hi!

I'm not sure how I feel about that. It feels like a good idea at first, but it might lead to dangerous behaviours.

Let me explain my thought: having such a feature would encourage people to use it (of course). Doing so can lead so side effects. For example,  if, in a project you're working on, you want to use a custom management command named "migrate_data_to_other_server", you might end up typing "./manage.oy migrate" in hope for the system to display the exact name that you probably have forgotten. But it won't, it will migrate your database instead. What I mean is that executing commands that shouldn't work on purpose might lead to executing the wrong command instead. And management commands might be dangerous if not used at the right time (I've seen management commands being used to push code to production for example. Executing them by error in a dev environment might be a real issue!).

I'd prefer to encourage the use of "./manage.py help", which lists all available commands, or use masks when searching for a command ("./manage.py migrate*"). When you want to look for the name of a command, you'd know that adding a star somewhere won't execute anything other than listing available commands matching the value you just gave. And every developer knows (I think) how to use wildcards.

-Brice


Le 15/07/17 à 18:36, Vláďa Macek a écrit :
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Tom Forbes

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Jul 17, 2017, 4:47:56 AM7/17/17
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Vlada:
I think this is a great idea for improving the usability of manage.py, especially for newcomers. When I looked your current implementation used a simple 'in' to find suggestions, but this is not great for the most obvious/common use case: typos.

I would strongly advocate for using the levenshtein distance algorithm if this does get merged, there are some simple and succinct python implementations we can use, and the algorithm itself is what git uses to suggest commands (and I've always found that quite good).

Brice: 
You are right in that this is a case that could happen in part due to this feature, but it's a long shot and IMO the benefits outweigh the risks. This can happen without this feature anyway - if someone is typing in random manage.py commands without thinking then issues can and will arise. The only preventative measure we could take would be to add an "are you sure?" prompt after every manage.py invocation which is not a great idea overall.

For newcomers though this could be great, seeing the 'command not found' message can be confusing and unhelpful, any help we can add to that is a good thing IMO. Adding stars to the command invocation can be even more confusing as users have to escape them (and if they don't they could end up running random commands) and it's not terribly nice UI wise.

Built in shell autocompletion would be the best way forward in this case, at least for non-windows users. Kubectl has a nice way of doing this: source <(kubectl completion bash|zsh). Maybe something like this could be adapted for manage.py?


On 17 Jul 2017 08:49, "Brice PARENT" <con...@brice.xyz> wrote:

Hi!

I'm not sure how I feel about that. It feels like a good idea at first, but it might lead to dangerous behaviours.

Let me explain my thought: having such a feature would encourage people to use it (of course). Doing so can lead so side effects. For example,  if, in a project you're working on, you want to use a custom management command named "migrate_data_to_other_server", you might end up typing "./manage.oy migrate" in hope for the system to display the exact name that you probably have forgotten. But it won't, it will migrate your database instead. What I mean is that executing commands that shouldn't work on purpose might lead to executing the wrong command instead. And management commands might be dangerous if not used at the right time (I've seen management commands being used to push code to production for example. Executing them by error in a dev environment might be a real issue!).

I'd prefer to encourage the use of "./manage.py help", which lists all available commands, or use masks when searching for a command ("./manage.py migrate*"). When you want to look for the name of a command, you'd know that adding a star somewhere won't execute anything other than listing available commands matching the value you just gave. And every developer knows (I think) how to use wildcards.

-Brice


Le 15/07/17 à 18:36, Vláďa Macek a écrit :
Hi everyone,

I had an idea that would save me time working with Django:

The manage.py wouldn't only print "Unknown command" when incomplete subcommand name given, but also print those available by substring search.

https://code.djangoproject.com/ticket/28398

I added a screenshot and a patch there.

In my opinion, such first implementation could be as simple as that. Smarter versions may come later.

As suggested by Tim Graham (thanks, Tim), I resort here for opinions.

Thank you,

Vlada Macek

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Brice PARENT

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Jul 17, 2017, 4:59:59 AM7/17/17
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I agree what I proposed wasn't either the best solution. It was more a workaround not to fall into the problem I mentioned.

Maybe then, when the command is not found, we could make something like the following (based on Vlada's work) :

$./manage.py passw
Unknow command "passw"
Would you like to look for commands looking like this? [Y/n] Y
Executing "./manage.py help | grep passw" (or "./manage.py search_command passw")
Candidate commands:
- changepassword [user]
- password
- setadminpassword

or something like that. It helps the user learn what he should use to look for a command's name instead of making user's errors a feature.

-Brice


Le 17/07/17 à 10:47, Tom Forbes a écrit :
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Adam Johnson

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Jul 17, 2017, 5:32:09 AM7/17/17
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I feel like this mostly duplicates the bash completion logic we have, which is also more standard across other CLI's

However I agree with Tom that correcting for typos is the main use case, using levehshtein distance is a good idea.

Another thing that some CLI's have, like npm or arc is auto-correction for common typos, e.g. ./manage.py mgriate could print out a message 'Assuming you meant migrate' and then continue executing migrate, not sure if this is the best for Django though where commands can be arbitrarily added by third party apps.



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Tom Forbes

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Feb 16, 2018, 1:22:33 PM2/16/18
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Did we reach a consensus on this? Would it change things if this could be implemented with a very small changeset?

People brought up that it seems similar to the bash completion - perhaps we can share code between the two features? I think it's a great idea from a usability standpoint, and seeing another junior engineer start to use manage.py I think it could make a difference to beginners.

I've made a simple PR that uses the stdlib 'difflib.get_close_matches' which seems to be pretty great at suggesting the right command and it's also less code to maintain: https://github.com/django/django/pull/9703

With this the output 'manage.py rnserver' would be:

Unknown command 'rnserver'. Did you mean runserver?
Type 'manage.py help' for usage.

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