[1.5.0] Is it possible to provide a type callable access to self from within a command set, similar to how choices_method works? #1243

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1. kmvanbrunt commented on Jul 22, 2022

   

   kmvanbrunt

   on Jul 22, 2022

   Last edited by kmvanbrunt

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   Since the parser is created before the CommandSet instance, type is pointing at an unbound method.
   This is the same for tab completion methods like choice_provider. Command parsers are basically class objects, not instance objects.

   cmd2 gets around this for tab completion methods since they're called in our custom code and we pass self manually as the first argument to the unbound method. All the type stuff is run by argparse, and it's basically just used as a cast. See https://github.com/python/cpython/blob/3.10/Lib/argparse.py#L2484.

   If you want argparse to call the bounded type method, then you need to set type after the CommandSet instance is created. That way the method will be bounded to an instance and self is already populated when called.

   Here is 1 option.

   class MyCommandSet(CommandSet):
       def __init__(self) -> None:
           super().__init__()
   
           # Set the argument's type using the bounded method
           MyCommandSet.saved_arg.type = self.custom_type
   
       parser = Cmd2ArgumentParser("Example")
   
       # Save this argument so we can edit it later in __init__()
       saved_arg = parser.add_argument(..., choices_method=my_choices)
   
       @with_argparser(parser)
       def do_blah(self, args: argparse.Namespace):
          ...

   👍React with 👍1Reacted by Devon DeJohn
2. ddejohn commented on Jul 22, 2022

   

   ddejohn

   on Jul 22, 2022

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   Just to clarify, you've got saved_arg but then in the __init__ you're setting the type of MyCommandSet.my_arg. This is just a typo, right?
3. kmvanbrunt commented on Jul 22, 2022

   

   kmvanbrunt

   on Jul 22, 2022

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   @ddejohn Yes, that is a typo. I've corrected the code now.

   👍React with 👍1Reacted by Devon DeJohn
4. python-cmd2

   locked and limited conversation to collaborators on Sep 12, 2022
5. anselor

   converted this issue into a discussion #1247 on Sep 12, 2022