Command with a default arg fails to run when omitting the argument

[alpinweis]

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I am running...

• Errbot version: 6.1.6
• OS version: ubuntu 18.04
• Python version: 3.6.9
• Using a virtual environment: docker
• Backend: slack

Issue description

I have a command with an argument. I'd like it to work with a default value if the argument is omitted.

@arg_botcmd("service_name", type=str, default="myservice", help="Service name")
def getstatus(self, msg, service_name):
  ...

I get an error when I try to run it w/o an argument.

User: !getstatus myservice
Errbot: ok

User: !getstatus
Errbot: I couldn't parse the arguments; the following arguments are required: service_name

The correct/expected result would be for the command to pick the default value myservice for the missing argument service_name. I also tried to use a default arg value in the method signature, but it did not help.

def getstatus(self, msg, service_name="myservice"):

[duhow]

As how the arg_botcmd is working now, first argument creates the ArgumentParser object, and does not allow setting the required flag you're looking for. https://docs.python.org/3/library/argparse.html#required

https://github.com/errbotio/errbot/blob/54542fd38250b4cb977283854c5cb2b446b1281b/errbot/__init__.py#L383-L386

But the next ones can use the argparse options. https://github.com/errbotio/errbot/blob/54542fd38250b4cb977283854c5cb2b446b1281b/errbot/__init__.py#L445