a method to open up a terminal inside a running container

        :param container_alias: string with name or id of container 
        :return: None

def enter(self, container_alias):

        '''
            a method to open up a terminal inside a running container

        :param container_alias: string with name or id of container 
        :return: None
        '''
        
        title = '%s.enter' % self.__class__.__name__

    # validate inputs
        input_fields = {
            'container_alias': container_alias
        }
        for key, value in input_fields.items():
            object_title = '%s(%s=%s)' % (title, key, str(value))
            self.fields.validate(value, '.%s' % key, object_title)
    
    # compose system command
        from os import system
        sys_cmd = 'docker exec -it %s sh' % container_alias
        if self.localhost.os.sysname in ('Windows'):
            sys_cmd = 'winpty %s' % sys_cmd

    # open up terminal
        system(sys_cmd)