Return new Command object that will be run with additional
        environment variables.

        Specify environment variables as follows:

            new_cmd = old_cmd.with_env(PYTHON_PATH=".", ENV_PORT="2022")

def with_env(self, **environment_variables):
        """
        Return new Command object that will be run with additional
        environment variables.

        Specify environment variables as follows:

            new_cmd = old_cmd.with_env(PYTHON_PATH=".", ENV_PORT="2022")
        """
        new_env_vars = {
            str(var): str(val) for var, val in environment_variables.items()
        }
        new_command = copy.deepcopy(self)
        new_command._env.update(new_env_vars)
        return new_command