Disable invalid value for a setting

[pihentagy]

I managed to create an autocompletable settable:

        env_settable = Settable('env', str, 'Your environment', self,
            choices_provider=list_envs, onchange_cb=self._env_changed)
        self.add_settable(env_settable)

    def _env_changed(self, param_name, old, new):
        if new not in list(config.get_config()['environments'].keys()):
            self.env = old

Almost there, but is there a way to correctly refuse to set an invalid setting?
Now the prompt lies (telling the new env is eee, but it's not), as _env_changed runs too late.

FTA> set env eee
env - was: 'dev'
now: 'eee'
FTA> set env
Name  Value                           Description                                                 
==================================================================================================
env   dev                             Your environment                                            
FTA> 

[kmvanbrunt]

To validate a Settable's value, use val_type and not onchange_cb.

val_type is a function which runs when setting the value. Whereas onchage_cb, as you've already noticed , runs after the Settable has been set to the new value.

Here is val_type's docsctring.

:param val_type: callable used to cast the string value from the command line into its proper type and
                 even validate its value. Setting this to bool provides tab completion for true/false and
                 validation using to_bool(). The val_type function should raise an exception if it fails.
                 This exception will be caught and printed by Cmd.do_set().

So in your case, instead of setting val_type to str, set it to a validator function like validate_env which is implemented below. Raising an exception prevents the Settable from being changed and prints an error to the user.

def validate_env(new_val: str) -> str:
    valid_vals = list(config.get_config()['environments'].keys())
    if new_val not in valid_vals:
        raise ValueError(f"invalid choice: {new_val!r} (choose from {valid_vals})")
    return new_val