How to use the esphome.codegen.get_variable function in esphome

def register_uart_device(var, config):
    """Register a UART device, setting up all the internal values.

    This is a coroutine, you need to await it with a 'yield' expression!
    """
    parent = yield cg.get_variable(config[CONF_UART_ID])
    cg.add(var.set_uart_parent(parent))

if CONF_ECO2 in config:
        sens = yield sensor.new_sensor(config[CONF_ECO2])
        cg.add(var.set_eco2_sensor(sens))

    if CONF_TVOC in config:
        sens = yield sensor.new_sensor(config[CONF_TVOC])
        cg.add(var.set_tvoc_sensor(sens))

    if CONF_BASELINE in config:
        cg.add(var.set_baseline(config[CONF_BASELINE]))

    if CONF_COMPENSATION in config:
        compensation_config = config[CONF_COMPENSATION]
        sens = yield cg.get_variable(compensation_config[CONF_HUMIDITY_SOURCE])
        cg.add(var.set_humidity_sensor(sens))
        sens = yield cg.get_variable(compensation_config[CONF_TEMPERATURE_SOURCE])
        cg.add(var.set_temperature_sensor(sens))

def sensor_in_range_to_code(config, condition_id, template_arg, args):
    paren = yield cg.get_variable(config[CONF_ID])
    var = cg.new_Pvariable(condition_id, template_arg, paren)

    if CONF_ABOVE in config:
        cg.add(var.set_min(config[CONF_ABOVE]))
    if CONF_BELOW in config:
        cg.add(var.set_max(config[CONF_BELOW]))

    yield var

def to_code(config):
    var = cg.new_Pvariable(config[CONF_OUTPUT_ID])
    yield cg.register_component(var, config)

    fan_ = yield fan.create_fan_state(config)
    cg.add(var.set_fan(fan_))
    output_ = yield cg.get_variable(config[CONF_OUTPUT])
    cg.add(var.set_output(output_))

    if CONF_OSCILLATION_OUTPUT in config:
        oscillation_output = yield cg.get_variable(config[CONF_OSCILLATION_OUTPUT])
        cg.add(var.set_oscillating(oscillation_output))

def to_code(config):
    var = cg.new_Pvariable(config[CONF_ID])
    time_ = yield cg.get_variable(config[CONF_TIME_ID])
    cg.add(var.set_time(time_))
    cg.add(var.set_latitude(config[CONF_LATITUDE]))
    cg.add(var.set_longitude(config[CONF_LONGITUDE]))

    for conf in config.get(CONF_ON_SUNRISE, []):
        trigger = cg.new_Pvariable(conf[CONF_TRIGGER_ID])
        yield cg.register_component(trigger, conf)
        yield cg.register_parented(trigger, var)
        cg.add(trigger.set_sunrise(True))
        cg.add(trigger.set_elevation(conf[CONF_ELEVATION]))
        yield automation.build_automation(trigger, [], conf)

    for conf in config.get(CONF_ON_SUNSET, []):
        trigger = cg.new_Pvariable(conf[CONF_TRIGGER_ID])
        yield cg.register_component(trigger, conf)
        yield cg.register_parented(trigger, var)

def to_code(config):
    hub = yield cg.get_variable(config[CONF_ESP32_TOUCH_ID])
    var = cg.new_Pvariable(config[CONF_ID], config[CONF_NAME], TOUCH_PADS[config[CONF_PIN]],
                           config[CONF_THRESHOLD])
    yield binary_sensor.register_binary_sensor(var, config)
    cg.add(hub.register_touch_pad(var))

def esp8266_set_frequency_to_code(config, action_id, template_arg, args):
    paren = yield cg.get_variable(config[CONF_ID])
    var = cg.new_Pvariable(action_id, template_arg, paren)
    template_ = yield cg.templatable(config[CONF_FREQUENCY], args, float)
    cg.add(var.set_frequency(template_))
    yield var

def to_code(config):
    var = cg.new_Pvariable(config[CONF_ID])
    yield cg.register_component(var, config)
    yield switch.register_switch(var, config)

    pin = yield cg.gpio_pin_expression(config[CONF_PIN])
    cg.add(var.set_pin(pin))

    cg.add(var.set_restore_mode(config[CONF_RESTORE_MODE]))

    if CONF_INTERLOCK in config:
        interlock = []
        for it in config[CONF_INTERLOCK]:
            lock = yield cg.get_variable(it)
            interlock.append(lock)
        cg.add(var.set_interlock(interlock))
        cg.add(var.set_interlock_wait_time(config[CONF_INTERLOCK_WAIT_TIME]))

def cat9554_pin_to_code(config):
    parent = yield cg.get_variable(config[CONF_CAT9554])
    yield CAT9554GPIOPin.new(parent, config[CONF_NUMBER], config[CONF_MODE], config[CONF_INVERTED])

def to_code(config):
    parent = yield cg.get_variable(config[CONF_CLIMATE_ID])
    var = cg.new_Pvariable(config[CONF_ID])
    yield sensor.register_sensor(var, config)
    yield cg.register_component(var, config)

    cg.add(var.set_parent(parent))
    cg.add(var.set_type(config[CONF_TYPE]))