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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def validate(self, settings):
 """Raise ValidationError if invalid"""


        if self.envs is None:
            self.envs = [settings.current_env]

        if self.when is not None:
            try:
                # inherit env if not defined
                if self.when.envs is None:
                    self.when.envs = self.envs

                self.when.validate(settings)
            except ValidationError:
                # if when is invalid, return canceling validation flow
                return

        # If only using current_env, skip using_env decoration (reload)
        if (
            len(self.envs) == 1
            and self.envs[0].upper() == settings.current_env.upper()
        ):
            self._validate_items(settings, settings.current_env)
            return

        for env in self.envs:
            with settings.using_env(env):
                self._validate_items(settings, env)